Role of Methylenetetrahydrofolate Reductase (Mthfr), Glutathione
Journal of Hematology & Thromboembolic Diseases

Journal of Hematology & Thromboembolic Diseases
Open Access

ISSN: 2329-8790

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Review Article - (2013) Volume 1, Issue 1

Role of Methylenetetrahydrofolate Reductase (Mthfr), Glutathione S-transferases (Gsts M1 and T1) and Haptoglobin (Hp) Gene Polymorphisms in Susceptibility to Chronic Myeloid Leukemia (Cml)

Ana Luisa Miranda-Vilela1* and Graciana Souza Lordelo1,2
1Department of Genetics and Morphology, Institute of Biological Sciences, University of Brasilia (UnB), Brasilia/DF, Brazil
2Haematology and Haemotherapy Services of the Hospital de Base of Federal District (NHH/HBDF), Brasilia/DF, Brazil
*Corresponding Author: Ana Luisa Miranda-Vilela, Department of Genetics and Morphology, Institute of Biological Sciences, University of Brasilia (UnB), Brasilia/DF, Brazil, Tel: +55 61 3107-3085, Fax: +55 61 3107-2923 Email: ,


Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm derived from an abnormal pluripotent hematopoietic stem cell that underwent a chromosomal translocation t(9;22)(q34;q11) acquiring the BCR-ABL1 fusion gene, also known as the Philadelphia chromosome. Although the clinical and biological aspects are well documented, little is known about individual susceptibility to CML. There are no known hereditary, familial, geographic, ethnic, or economic associations with CML, and the mechanisms behind disease progression are not fully understood. However, while a specific chromosomal translocation is the common oncogenetic mechanism of CML, it may have environmental causes such as irradiation and chemical (e.g., benzene) exposure, which exert toxicity via pro-oxidant mechanisms. Oxidative stress has been observed in several hematopoietic malignancies, including acute and chronic myeloid leukemias. It is known that BCR/ABL expression stimulates reactive oxygen species (ROS) production in hematopoietic progenitor cells, and studies have suggested that ROS may contribute to increased DNA damage in CML cells. Leukemia cell lines expressing BCR-ABL1 kinase accumulate ROS and oxidative DNA damage, resulting in genomic instability, which leads to the disease relapse and/or malignant progression to a fatal blast phase. These suggest a probable genetic susceptibility to this disease related to the body’s ability to defend itself from external aggression such as chemicals, ionizing radiation and others, through functional polymorphic variant enzymes that metabolize toxicants and/or protect against oxidative stress. Thus, this review aims to address a comprehensive summary of CML, including the physiological function of the normal proteins encoded by the ABL1 and BCR genes and the oncogenetic mechanism of the BCR-ABL1 fusion proteins, as well as to discuss the role of polymorphisms in methylenetetrahydrofolate reductase (MTHFR), glutathione S-transferases (GSTs M1 and T1) and haptoglobin (Hp) genes in the susceptibility to Chronic Myeloid Leukemia (CML).

Keywords: Chronic myeloid leukemia (CML); Philadelphia chromosome (Ph) chromosome; CML susceptibility; Genetic polymorphisms


Chronic myeloid leukemia (CML), also known as chronic myelocytic or chronic myelogenous leukemia, is a clonal myeloproliferative disorder characterized by expansion of transformed, primitive hematopoietic progenitor cells. It was first recognized as a clinical entity by John Hughes Bennett in the mid-1840s [1-4]. The myeloid progenitor cells expand in various stages of maturation, being released into the peripheral blood and subsequently following to extramedullary sites. The disorderly sprawl of these cells reflects the occurrence of alterations in their proliferative capacity, as well as changes in the balance between self-renewal and differentiation, increasing the number of transformed cells, and reducing the number of pluripotent stem cells [1,4].

CML can be classified into three disease phases: chronic phase (CP), accelerated phase (AP), and terminal blast phase (BP). Approximately 90% of patients are diagnosed during the CP, although in this phase 20% to 40% of patients may remain asymptomatic [3,5-7]. Common symptoms of CML in CP, when present, are generally related to the expansion of CML cells, and mainly include fatigue, weakness, headaches, weight loss, malaise, easy satiety and discomfort or left upper quadrant pain, caused primarily by anemia and splenomegaly [3,6], although most patients do not present anemia in the diagnosis and, in general, their quality of life is not altered in this phase, especially if the leukocyte count is controlled [8]. Most patients have basophilia and eosinophilia [7]. Neutrophilic leukocytosis is also a common feature of CP [9], and the white blood cell (WBC) count can be as high as 100,000 cells/mL, leading in rare instances to signs and symptoms of hyperviscosity, such as retinal hemorrhage, priapism (usually with marked leukocytosis or thrombocytosis), cerebrovascular accidents, upper gastrointestinal ulceration and bleeding (from elevated histamine levels due to basophilia). Also common is the occurrence of platelet dysfunction [3,6].

Before introduction of tyrosine kinase inhibitors (TKI) (1973- 2000) [10], the median survival of patients with CML after diagnosis was 4-6 years, and the stages following the CP had a short duration, corresponding to the terminal period of the disease [8], with AP lasting 4 to 6 months and BP, a few months [11]. Nowadays (post TKI era), the median survival of patients has increased to 13-15 years for CP, and 6-12 months for both AP and BC [12,13]. However, although progression through all stages is most common, the time course for progression can be extremely varied, and 20% to 25% of patients progress directly from CP to BP [5].

CML constitutes about 15-20% of all newly diagnosed cases of leukemia in adults and occurs with an incidence of approximately 1-2 cases in 100,000/year, with an estimated survival rate of 90% at 5 years and an annual mortality rate of 2% [3,6,7,9,14]. The median age of onset of CML is about 40-60 years, with less than 10% of the cases in patients aged less than 20 years [7,9,15]. It is more common among men than women, with a male-to-female ratio of 1.4 to 2.2:1 [16]. Although the clinical course has been described as being similar in both sexes [16], a recent analysis performed by Mandal et al. [10] from the Surveillance Epidemiology and End Results of the US National Cancer Institute (SEER) to see survival differences from the pre-TKI (1973-2000) to post-TKI eras (2002-2008) showed that, although the survival rates of the older population were lower than the younger population for each group (for both pre and post-TKI era), and there was a relative survival increase from the pre- to post-TKI era for all ethnic groups, the survival rate of young African-American men (<50 years) was significantly lower compared to young Caucasian men in the pre-TKI era, while young African-American women (<50 years) with CML had lower relative survival rates compared to young Caucasian women in the postimatinib era. According to the authors, while socioeconomic status and access to healthcare have been known to impact survival in the past, which could explain the lower survival in African-American men that we observed in the pre-TKI era, in the post-TKI era higher rates of imatinib resistance in the African-American group could explain the lower relative survival rates observed for African-American women [10]. This means that at least among young women with CML using TKI, the ethnic differences should be taken into account in association studies involving CML. Also for men <50 years, such ethnic differences take into account underdeveloped and developing countries, where socioeconomic status and access to healthcare still can cause an impact on survival.

CML Etiology

The etiology of CML is related to a chromosomal translocation, discovered by Nowell and Hungerford, on observing an anomalous chromosome of group G [17], the Philadelphia chromosome, often abbreviated as Ph, Ph(1), or Ph1, and present in 95% of individuals affected [4,18]. With the improvement of chromosome banding techniques, Rowley [19] described the chromosomal abnormality that exists in these patients with CML as a reciprocal translocation between two chromosomes, where chromosome 22 shows loss of the terminal portion of its long arm and chromosome 9 presents a gain of this genetic material in the terminal portion of its long arm.

The classic definition of Ph chromosome is t(9;22)(q34;q11), which indicates that this chromosome results from a reciprocal translocation of cytogenetic material following a break on chromosome 9 at band q34, and a break on chromosome 22 at band q11 [1,4,5,9,20,21]. As a result of these breaks, the 3’ part of the ABL1 (Abelson murine leukemia viral oncogene homolog 1) gene is moved from chromosome 9 (its normal locus) to chromosome 22, and is juxtaposed to a segment of the BCR (Breakpoint Cluster Region) gene on chromosome 22. The BCR gene is also disrupted, and its 3’ end is moved from chromosome 22 to chromosome 9, while its 5’ domain remains on chromosome 22 [6,9]. Thus, the Ph chromosome has a chimeric gene resulting from the fusion of the 5’ end closer to the centromere of the BCR gene on chromosome 22q11.23, with the 3’ end of the exon 2 (known as a2) of the ABL1 protooncogene, located at chromosome 9q34.1 (Figure 1). This configuration places the fusion gene under the control of the BCR promoter [1,9,20]. The hybrid BCR/ABL oncogene encodes a constitutively active BCR-ABL fusion tyrosine-kinase protein, which has a direct and crucial participation in the development of CML, by stimulating uncontrolled proliferation of transformed cells, alteration in the balance of self-renewal/differentiation (discordant maturation) and in cell adhesion properties, and escape from apoptosis, generating genomic instability and leading to mutations and chromosomal abnormalities [4,6,2024].


Figure 1: Schematic representation of translocation t(9;22)(q34;q11) in CML showing the typical breakpoint regions, their fusion transcripts M-bcr, m-bcr and μ-bcr and related fusion proteins.

It is known that the variation of breakpoints of the BCR gene involved in translocation between chromosomes 9 and 22 can promote the formation of different transcripts of BCR/ABL genes and their products, but all BCR/ABL1 fusion genes contain a variable 5’ portion derived from BCR sequences and a 3’ portion almost invariably of the ABL1 gene sequence [25,26]. Heisterkamp et al. [27] determined the structural organization of the BCR gene, which contains 23 exons and occupies a region of about 130 kb on chromosome 22. In the vast majority of CML patients, the break on chromosome 22 involves an area of 5.8 kilobases (kb) termed the major breakpoint cluster region (M-bcr), which contains five exons corresponding to exons 12 to 16, originally numbered from b1 to b5 [26]. The breaks occur within introns located downstream of either exon 13 (known as e13 or b2) or 14 (known as e14 or b3) with the introns upstream of ABL1 exon 2 (a2) forming the fusion gene b2a2 or b3a2, respectively. This rearrangement generates a BCR/ABL1 hybrid gene that is expressed as an 8.5 kb chimeric mRNA with a b2a2 or b3a2 junction, and translated into a 210 kilodaltons (kDa) fusion protein (p210BCR-ABL), which is associated with the underlying mechanism in the chronic phase of CML [4,20,26,28-30]. The breakpoint in the BCR gene is also found within the M-bcr region (p210) in 30% of adults and 20% of children with Philadelphia chromosome-positive (Ph+) Acute Lymphoblastic Leukemia (Ph+ ALL), as well as in patients with Acute Myeloid Leukemia (AML) [31-35]. There are also two less common breakpoints in the intronic region between the alternative BCR exon 2 known as minor breakpoint cluster region (m-bcr), and between BCR exons 19 and 20, known as microbreakpoint cluster region (μ-bcr), which encode, respectively, a 190-kDa (p190BCR-ABL, e1a2 transcripts) and a 230-kDa (p230BCR-ABL, e19a2 transcripts) fusion protein (Figure 1) [28,29]. Transcript e1a2 (p190) rarely occurs in CML patients and it has been associated with an inferior outcome to therapy with tyrosine kinase inhibitors, but it is commonly found in Ph+ ALL patients and occasionally in AML. Junctions e19 and e20 (p230) also rarely occur in CML or in a clinical entity called neutrophilic CML; the latter has been reported to have a more benign clinical course than that associated with the traditional b2/a2 or b3/a2 fusion (p210) [31,32,36].

Although 5% of cases of CML do not exhibit the Ph chromosome in classical cytogenetic analysis, molecular analysis detects BCR/ABL rearrangements in most cases [18]. As patients progress through the different phases, a distinct feature of disease progression is the appearance of additional cytogenetic abnormalities in the Ph+ cells [5]. This phenomenon, known as clonal evolution, frequently involves a second Ph (30%), trisomy of chromosome 8 (33%), isochromosome 17 (20%), trisomy of chromosome 21 (7%) and monosomy of chromosome 7 (5%), besides other chromosome abnormalities [3739]. Mutations and deletions may also occur in specific genes that regulate the cell cycle (eg. INK4A, ARF, p16/INK4a, CDKN2A-CDKN2B, p53 and RB) [1,5,18,40,41], as well as in IKAROS and PAX5 genes [37], required for normal lymphoid development [41,42], thereby facilitating leukaemiainitiating cell self-renewal and enhancing targeted therapeutic resistance in vivo [40]. Thus, as previously mentioned, the BCR/ABLtransformed cell seems endowed with an intrinsic genetic instability, which leads to a progressive accumulation of genetic lesions. This progression represents the natural end of all CML cases and the main cause of death in CML patients [18].

The proteins generated from different breakpoints have been the subject of a number of studies, many of which, seeking a better understanding of CML, focused on investigating the physiological function of the proteins encoded by the ABL1 and BCR genes.

Proteins encoded by the normal ABL1 and BCR genes

The normal ABL1 gene encodes the c-ABL1 protein (145 kDa), which belongs to the Scr family of non-receptor tyrosine kinases. This protein is ubiquitously expressed in the cell membrane, actin cytoskeleton, cytosol and nucleus, regulating various cellular processes, such as mitogenesis, migration, adhesion, response to DNA damage, survival and response to oxidative stress [43]. The structural organization of c-ABL1 domains is similar to the Src protein kinase (Avian Sarcoma), having SH1 tyrosine kinase (Src Homology 1), SH2 and SH3 domains toward the N-terminus. At the C-terminal end, the c-ABL molecule has a sequence rich in proline (PXXP), which interacts with SH3 domains of adapter proteins; a DNA binding site; a binding site for both F-actin and G-actin; a nuclear localization signal (NLS); and a nuclear export signal (NES) (Figure 2) [44]. Because of its potentially deleterious effects, the tyrosine kinase activity of c-ABL1 must be very tightly controlled in the cell. This is achieved by autoinhibition through a complex set of intramolecular interactions that involve the SH3 and SH2 domains, the catalytic tyrosine kinase domain, and all other segments in the aminoterminal half of the protein. The autoinhibited form of c-ABL1 is not phosphorylated on tyrosine residues [45].


Figure 2: Schematic representation of the structural organization of c-ABL1.

The BCR gene is also expressed ubiquitously, and encodes a 1271 amino acid cytoplasmic phosphoprotein of 160 kDa molecular mass, found primarily in the brain and hematopoietic cells at early stages of myeloid differentiation, and whose levels are significantly reduced in mature polymorphonuclear leukocytes [4,20]. In the first exon-encoded sequences (amino acids 1-427), BCR contains a coiled-coil domain that mediates homo-oligomerization, and a domain of serine/threonine kinase activity containing SH2-binding domains (noncatalytic regions of ~100 amino acids that bind SH2-binding sites), where other proteins can bind to the phosphoamino acid serine, threonine, or tyrosine (rather than only tyrosine). This interaction is important in the assembly of signal transduction [4,20,46]. A consensus sequence homologous to the ATP-binding site of other kinases as well as a likely phosphotransferase domain has also been identified, allowing BCR to autophosphorylate on serine and threonine residues, as well as to transphosphorylate casein and histones (known substrates for serine/threonine kinases) in vitro [20]. The central region of the BCR protein (amino acids 490 to 690; encoded by exons 3 to 10) contains a region of homology to the DBL oncoprotein (with an associated pleckstrin homology domain) [4,46] that functions as a guanine nucleotide-exchange factor (GEF, that activates G proteins) for RHO proteins [4], a family of GTPases that has been intensively studied for their roles in signal transduction processes which lead to cytoskeletal-dependent responses, including cell migration and phagocytosis, besides being important regulators of cell cycle progression and affecting the expression of a number of genes, including those for matrix-degrading proteases implicated in cancer invasion [47]. This region can interact with the protein Xeroderma Pigmentosum group B protein (XPB), which plays an important role in DNA repair and cell cycle regulation [20,48]. The C-terminus of BCR, in turn, contains a domain with GTPase activating protein (GAP, which inactivates G proteins) homologous to the GAP protein for p21RHO (RhoGAP), which is involved in the regulation of the actin cytoskeleton, having GAP activity toward the Ras-related GTP-binding protein (p21RAC) and Cdc42 proteins (Figure 3) [4,20,49]. Although the normal function of the BCR gene product is not known and it has no intrinsic oncogenic properties [4], these data indicate that BCR has both GEF and GAP functions, suggesting a dual role for this molecule in G protein-associated signaling pathways, besides implicating the participation of BCR in two major intracellular signaling mechanisms in eukaryotic cells: phosphorylation and GTP-binding [20].


Figure 3: Schematic representation of the structural domains of the BCR protein.

BCR-ABL1 fusion proteins

The three principal forms of BCR-ABL1 fusion proteins (p190, p210, and p230) contain almost all c-ABL1 (except the first exonencoded sequence), including the entire ABL tyrosine kinase catalytic domain, but they have different amounts of BCR sequences: only p210 and p230 include the DBL/plekstrin homology domains from the central portion of BCR, and a portion of C-terminal GAP domain of BCR is retained only in the longer p230 fusion protein (it is not included in p190 and p210). However, the first exon-encoded sequence of the BCR gene is the one included in all known BCR-ABL fusion proteins (Figure 1) [4,20,31]. As mentioned above, within this region of BCR resides an oligomerization domain and the kinase domains containing SH2-binding domains [4,20,46]. The last allows the binding of BCR to the c-ABL1 SH2 sequences in the phosphoamino acids serine and threonine (but not phosphotyrosine residues on BCR) [20,50]. The BCR sequences involved in this interaction, which lie between amino acids 192-242 and 298-413, are essential for the activation of the c-ABL1 tyrosine kinase, and thus, for the oncogenic activation of BCR-ABL [20,46,50]. This occurs because the oligomerization domain of BCR mediates dimerization and/or tetramerization of BCR-ABL, allowing a phosphorylation activated by loop that stabilizes a conformation compatible with substrate binding and catalysis, stimulating self-phosphorylations [45]. Thus, all the three BCR-ABL isoforms have increased tyrosine kinase relative to c-ABL1, due to the addition of BCR exon 1 sequences to c-ABL1 [4]. BCR-ABL creates a constitutively active tyrosine kinase which activates several signal transduction pathways from the cytoplasm to the nucleus [51,52], which are also utilized by hematopoietic growth factors, including steel factor, thrombopoietin, interleukin-3, and granulocyte/macrophagecolony stimulating factor [52].

BCR-ABL signaling prevents down-regulation of cyclin-dependent kinase activity and cell cycle arrest after growth factor deprivation of hematopoietic progenitor cells, its expression being sufficient to induce G1-to-S phase transition, DNA synthesis, and activation of cyclindependent kinases in cells that were arrested in G0 by growth factor deprivation [53], besides inhibiting apoptosis through activation of a Ras-dependent signaling pathway [54]. Thus, the primary mitogenic activity of BCR-ABL, on stimulating the transformed hematopoietic growth factor-dependent cell lines to enter in the cell cycle, leads to growth factor independence [52,53].

Considering the primary structures of p190, p210, and p230, it would be plausible to suppose that P210 would have a higher tyrosine kinase activity due to the DBL/plekstrin homology domains which function as a GEF (that activates G proteins), and, thus, a higher oncogenic activity than p190, which in turn would have larger oncogenic activity than P230 (due to a portion of a GAP catalytic domain, which inactivates G proteins). However, as revised by Van Etten [4], p190 has been reported as having the highest intrinsic kinase activity, followed by p210 and p230, as well as being a parameter of CML relapse [55]; it is also associated with an inferior outcome to therapy with TKI and with high-risk patients [36]. A possible explanation would be that the signal transducer and activator of transcription STAT6, a transcription factor normally activated by IL-4 and implicated in lymphoid proliferative responses, is preferentially tyrosine phosphorylated and activated by p190 (but not by p210) [31].

Role of Genetic Polymorphisms in CML Susceptibility

Although the clinical and biological aspects of CML are well documented, little is known about individual susceptibility to this disease [24]. There are no known hereditary, familial, geographic, ethnic, or economic associations with CML [3], and the mechanisms behind disease progression are not fully understood [5]. However, while a specific chromosomal translocation is the common oncogenetic mechanism of CML, it may have environmental causes such as irradiation [3,56] and chemical exposure to benzene [57-59] and other xenobiotics [58,60-62]. In most patients, the factor responsible for the induction of the Ph chromosome is unknown, although CML has been observed with increased frequency in individuals exposed to the atom bomb explosions of 1945 in Japan, in radiologists, and in patients with ankylosing spondylitis treated with radiation therapy [3], as well as still being diagnosed together with other oncohematological disorders in Ukrainian clean-up workers 10-18 years after the Chernobyl accident [56]. Moreover, benzene is a known human carcinogen, with a substantial number of case reports and epidemiological studies providing evidence of a causal relationship between occupational (chronic) exposure and various types of leukaemia [57,59]. An increased risk of CML has been reported after exposure to benzene, petrol refining products, polycyclic aromatic hydrocarbons, and electromagnetic fields among men [58], while a meta-analysis has confirmed an increased risk of CML related to pesticide applicators among men and farmers or agricultural workers [60], and associations between childhood leukemia with both parental occupational and residential pesticide exposure have been reported in review articles [61,62].

Oxidative stress, a state generated by an excessive production of reactive oxygen species (ROS) and/or by a deficiency in antioxidant pathways, has also been observed in several hematopoietic malignancies, including acute and chronic myeloid leukemias [63]. It is known that BCR/ABL expression stimulates ROS production in hematopoietic progenitor cells [64], and studies have suggested that ROS may contribute to increased DNA damage in CML cells [22]. Leukemia cell lines expressing BCR-ABL1 kinase accumulate ROS and oxidative DNA damage, resulting in genomic instability, which leads to disease relapse and/or malignant progression to a fatal blast phase [65]. These data suggest a probable genetic susceptibility to this disease, related to the body’s ability to defend itself from oxidative stress and/or external aggression such as chemicals, ionizing radiation and others, through functional polymorphic variant enzymes that metabolize toxicants and/or protect against oxidative stress. Thus, association studies have been performed to identify genetic variants associated with CML susceptibility, and among them are the polymorphisms in the genes of methylenetetrahydrofolate reductase (MTHFR) [24,66-74], glutathione S-transferases (GSTs M1 and T1) [24,74-87], and haptoglobin (Hp) [24,74,88-96], among others that will not be covered in this review.

Considering that: (1) as previously presented, it has been showed that there are differences among CML survival rates pre- and post- TKI by gender and race/ethnicity [10]; (2) the age-adjusted incidence and death rates of CML based on cases diagnosed in 2005-2009 in the U.S. population geographic areas also showed differences by gender and race/ethnicity as showed in table 1 [13], and this program is a population-based cancer register covering more than 25% of the U.S. population across several disparate geographical regions [10]; and (3) MTHFR, GSTs M1 and T1 and Hp polymorphisms vary among different ethnic groups as can be seen in tables 2-4; although we intend to outline the reasons for the possible influence of these polymorphisms on the susceptibility to CML and present the association studies related to them, studies in larger populations of patients and controls of both genders should be conducted in populations worldwide to better understand the biological significance of these polymorphisms in CML susceptibility in each ethnic group and by gender, as well as in understanding their role in the variability of the disease course and in responsiveness to therapeutic agents. This is because the conflicting results among the various association studies carried out in different ethnic groups focusing on the issue could be not due to ethnic differences but instead the result of methodological problems: several studies have analyzed relatively small groups of patients and controls, resulting in very broad intervals of statistical confidence of relative risks. Thus, although the influence of these polymorphisms in the susceptibility of CML is very plausible, worldwide studies involving larger populations of patients and controls by gender and race/ethnicity are necessary to avoid any doubt about the role of these polymorphisms in CML.

Race/Ethnicity Male Female
Incidence Rates (per 100,000 men) Death Rates (per 100,000 men) Incidence Rates (per 100,000 women) Death Rates (per 100,000 women)
White 2.1 0.4 1.2 0.2
Black 1.9 0.5 1.2 0.3
Asian/Pacific Islander 1.5 0.2 0.7 0.1
American Indian/Alaska Native 1.7 0.6 * *
Hispanic 1.7 0.3 1.1 0.2
*Statistic not shown. Rate based on less than 16 cases for the time interval

Table 1: The age-adjusted incidence and death rates of CML based on cases diagnosed in 2005-2009 in the U.S. population, by gender and race/ethnicity according to the Surveillance Epidemiology and End Results (SEER) of the National Cancer Institute [13].

Methylenetetrahydrofolate Reductase (Mthfr) C677t and A1298c Thermolabile Polymorphisms

DNA methylation, an essential epigenetic mechanism that plays critical roles in gene expression regulation, cell differentiation and genomic integrity, is catalyzed by methyltransferases, which use the universal methyl donor S-adenosyl-L-methionine (SAM) [97]. Methylenetetrahydrofolate reductase (MTHFR, EC, a key enzyme in homocysteine (Hcy) and folate metabolism, plays an important role in DNA methylation and provision of nucleotides for DNA synthesis [24]. MTHFR catalyzes the irreversible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the methyl donor for synthesis of methionine from homocysteine. Methionine in turn, is converted to SAM (Figure 4), which methylates specific cytosines in DNA, regulating gene transcription through methylation [24,97,98]. Because DNA hypomethylation has been linked to abnormal chromosome rearrangements [99], and methylation abnormalities also play a role in chromosome segregation processes in cancer cells [100], a decrease in MTHFR activity which results in hypomethylation may leads to alteration in chromosome recombination and abnormal chromosome segregation [101].


Figure 4: Folate metabolism, links to methionine-homocysteine metabolism, DNA synthesis and methylation.

On the other hand, the substrate of MTHFR, 5,10-methylenetetrahydrofolate, is also the cofactor for thymidylate synthase and is required for the production of deoxythymidine monophosphate (dTMP) via this enzyme [102]. The 5,10-methylenetetrahydrofolate donates a methyl group to deoxyuracil monophosphate (dUMP) converting it to dTMP (Figure 4), which is used for DNA synthesis and repair [103]. So, if folate is continually limited, low cytosolic levels of 5,10-methylenetetrahydrofolate decrease synthesis of dTMP, increasing the cellular ratio of dUMP/dTMP and thus the misincorporation of dUMP instead of dTMP during DNA replication [102,103]. As a result, the excision of uracil from DNA by uracil-DNA glycosylase and apyrimidinic endonuclease generates transient single-strand breaks (nicks) that could result in a less reparable and more hazardous double-strand break if two opposing nicks are formed [102]. This catastrophic repair cycle could lead to double-strand breaks and chromosomal damage [103], contributing to the increased risk of chromosomal aberrations and presumably the onset of the leukemogenic process associated with folate deficiency in humans [69,102,104]. Therefore, MTHFR also plays a role in providing nucleotides essential for DNA synthesis [105], because under situations of lower MTHFR activity, more 5,10-methylenetetrahydrofolate will be available for dTMP synthesis when in situations of folate deficiency status, preventing imbalances of nucleotide pools during DNA synthesis [24,106]. Thus, polymorphic variants of MTHFR that lead to enhanced dTMP pools and better quality DNA synthesis could promote some protection from the development of leukemia. This is particularly true of variants with translocations, but only if the activity of MTHFR is not reduced enough to cause DNA hypomethylation, and if the MTHFR variant does not affect plasma folate levels, which could lead to uracil misincorporation into DNA, especially in individuals with low folate intake.

In view of all the explanations, mutations in the MTHFR gene related to the decrease in MTHFR activity might explain the interindividual differences in the increase of chromosome breakage and damage. Therefore, the MTHFR gene is a good candidate for CML etiology [101].

The MTHFR gene is located on the short arm of chromosome 1 (1p36.3), and its complementary DNA (cDNA) sequence, which includes 11 exons ranging in size from 103 base pairs (bp) to 432 bp, is approximately 2.2 kb [107,108]. Several mutations in the MTHFR gene have been identified, but most are rare and associated with severe enzymatic deficiency [107]. However, in contrast with these rarities, two common thermolabile single-nucleotide polymorphisms (SNPs) in the MTHFR gene (C677T and A1298C) deserve special mention in CML susceptibility because they result in a decrease in MTHFR activity [109,110], and its possible consequent effects mentioned above.

It has been shown that the SNPs C677T (dbSNP rs1801133) and A1298C (dbSNP rs1801131) in the MTHFR gene are involved in increased meiotic chromosomal non-disjunction and risk of some aneuploidies, mainly Down’s syndrome [111-118]. Given that recurrent chromosomal abnormalities (such as a second Ph chromosome) added to new structural chromosome abnormalities and aneuploidies are important factors in the clonal evolution and pathogenesis of CML, where a large number of chromosome abnormalities are associated with the morphology and clinical subsets of CML, as well as its prognosis [37-39,101], the MTHFR C677T and A1298C polymorphisms are good candidates not only for CML etiology, but also for the chromosome abnormalities associated with the clonal evolution of CML, and thus for the disease progression and its consequent effects.

The transition C→T at nucleotide 677 (C677T; dbSNP rs1801133) in exon 4 of the MTHFR gene, resulting in the substitution of an alanine (GCC) for a valine (GTC) at position 222 (Ala222Val) in the N-terminal catalytic domain of the protein, which generates a thermolabile variant of the enzyme was first identified by Frosst et al. [98,108-110,119]. The 677TT homozygosis has been associated with reduced MTHFR activity and plasma folate levels, as well as elevated plasma Hcy concentrations (mild to moderate hyperhomocysteinemia), especially in patients with low folate levels [98,101,120]. It has been reported that MTHFR activity is reduced to 70% in homozygous TT and 30-40% in heterozygous CT with regard to the normal mean value [101,109,121]. Also, serum folate concentration is lower in individuals with the MTHFR 677TT genotype than in those with the MTHFR 677CC or 677CT genotypes [122]. Therefore, decrease in the MTHFR activity and serum folate levels in individuals carrying the MTHFR 677TT genotype could affect genomic stability by diminishing DNA methylation and favoring uracil misincorporation into DNA with its consequent double-strand breaks induced during DNA repair, mainly in condition of low folate intake.

The frequency of the MTHFR C677T polymorphism varies among ethnic groups. The C677T polymorphism is found in approximately 12% of the general population, with variations from 5% to 18% [98]. Analysis of Caucasian and Asian populations typically shows rates of ~12% for homozygous T/T and up to 50% for heterozygous C/T. African-Americans exhibit very low incidence of T/T genotype, whereas European Caucasians exhibit substantial variation [123].

The second polymorphism of the MTHFR gene, A1298C (dbSNP rs1801131), which occurs in exon 7, resulting in the replacement of glutamate (Glu or E) with alanine (Ala or A) at position 429 of the enzyme (Glu429Ala or E429A), was first identified by Van der Put et al. (1998) [108,110,124]. Since it lies in the SAM-regulatory domain of the enzyme (within the C-terminal regulatory domain) [24,98,108,124], the binding of SAM results in conformational changes within the MTHFR enzyme that inhibit the enzyme’s activity [108]. Thus, folate intake may affect MTHFR gene expression, regulating cellular SAM levels [98].

Although the MTHFR A1298C polymorphism has been observed in approximately 10% of individuals and is associated with reduced enzyme activity, it alone does not lead to a severe enzyme deficiency and does not seem to be associated with reduced plasma folate levels or elevated Hcy [98]. On the other hand, the combination of heterozygosis of both polymorphisms of MTHFR (C677T and A1298C) leads to features similar to those observed in homozygotes 677TT, and has been associated with reduced enzyme activity, decreased plasma folate levels and hyperhomocysteinemia [98,110].

Association studies between the MTHFR polymorphisms C677T and A1298C and risk of CML have been carried out in different populations, but several of them with conflicting results, as shown in table 2.

Although some of these studies were carried out with small samples mainly consisting of patients, where the previously mentioned methodological problems cannot be discarded, these conflicting results may also be due to: (1) studies considering folate intake are limited [122]; (2) individuals with the MTHFR 677TT genotype may need to consume more folate to maintain serum folate levels similar to those found in individuals with the 677CC/677CT genotypes [122]; and (3) the MTHFR A1298C polymorphism alone does not lead to a severe enzyme deficiency or reduced plasma folate levels [98,110]. Thus, studies involving serum folate and MTHFR C677T and A1298C polymorphisms adjusted for folate intake are needed to better understand the biological significance of these polymorphisms in CML susceptibility, as well as in understanding the variability of the disease course and the patients’ response to medication. Moreover, since these polymorphisms vary among ethnic groups (Table 2) and populations worldwide vary considerably in their predisposition to diseases and in the allele frequencies of pharmacogenetically important loci, probably due to genetic drift or adaptation to local selective factors such as climate and available nutrients [125], studies dealing with a large population in several ethnicities are also required to reach this understanding.

Authors, year Ethnicity Polymorphisms Characteristics of cases Characteristics of controls Polymorphisms Case Control OR (95% CI) P value
Robien et al., 2004 [66] Caucasians MTHFR C677T A1298C 336 CML patients The majority (86%) of the study population had a diagnosis of CML in chronic phase at the time of HCT. MTHFR C677T        
677CC 149(44)      
677CT 137(41)      
677TT 50(15)
MTHFR A1298C        
1298AA 155(46)      
1298AC 137(41)      
1298CC 44(13)      
Hur et al., 2006 [67] East  Asian MTHFR C677T A1298C 40 CML patients 200 healthy individuals without any clinical disorder as normal controls MTHFR C677T        
677CC 13(32.5) 80(40) 1.0
677CT 17 (42.5) 80(40) 1.31 (0.60-2.87)
677TT 10(25) 40(20) 1.54 (0.62-3.81)
MTHFR A1298C        
1298AA 31(77.5) 116(58) 1.0
1298AC 7(17.5) 78(39.0) 0.34 (0.14-0.80)
1298CC 2(5.0) 6(3.0) 1.25 (0.24-6.49)
Moon et al., 2007 [68] East  Asian MTHFR C677T A1298C 115 patients with CML (75 males, 40 females; mean age: 43.8 years The control subjects included 434 healthy individuals (195 males, 239 females; mean age: 47.3 years; MTHFR C677T        
677CC 43(37.4) 144(33.2) 1.00
677CT 45(39.1) 196(45.2) 0.77 (0.48-1.23) 0.27
677TT 27(23.5) 94(21.7) 0.96 (0.56-1.66) 0.89
MTHFR A1298C        
1298AA 74(64.3) 307 (70.7) 1.00
1298AC 33(28.7) 120(27.6) 1.11 (0.70-1.78) 0.65
1298CC 8(23.5) 7 (1.6) 5.12 (1.75-14.9) 0.003
Barbosa et al., 2008 [69] Mixed MTHFR C677T A1298C 27 CML patients (15 female (53.6%) and 13 male (46.4%); median age 27 yrs The control group consisted of 100 (47%  female and 53% male; median age 29 yrs. MTHFR C677T        
677CC 46(68.7) 65(65) 1
677CT 19(28.3) 29(29) 0.97 (0.46- 2.03)
677TT 2(3) 6(6) 0.48 (0.07- 2.76)
MTHFR A1298C        
1298AA 41(61.1) 63(63) 1.0
1298AC 23(34.3) 32(32) 1.11 (0.55- 2.25)
1298CC 3(4.6) 5(5) 0.89 (0.16- 4.48)
Kim et al., 2009 [70] Korea MTHFR C677T A1298C 149 CML patients (94 men and 55 women; mean age 50.4±17.1 years The control group (n = 1700 48.8% of the eligible subjects; 821 men and 879 women), mean age 52.2±14.3 years, underwent clinical examinations. MTHFR C677T        
677CC 54(36) 540(32) 1
677CT 72(47) 863(51) 0.81 (0.55-1.17) 0.26
677TT 26(17) 297(17) 0.90 (0.55-1.47) 0.67
MTHFR A1298C        
1298AA 97(64) 1147(68) 1
1298AC 49(33) 500(29) 1.15 (0.80-1.66) 0.44
1298CC 5(3) 53(3) 1.11 (0.43-2.85) 0.83
Ismail et al., 2009 [71] Jordan MTHFR C677T A1298C 149 patients diagnosed with CML were collected The control group consisted of 170 healthy individuals. MTHFR C677T        
677CC 63 (42.2) 94 (55.3) 1
677CT 67 (45.0) 66 (38.8) 1.52 (0.95-2.41) 0.081
677TT 19 (12.8) 10 (5.90) 2.84 (1.24-6.50) 0.014
MTHFR A1298C        
1298AA 59 (39.6) 76 (44.7) 1
1298AC 68 (45.6) 81 (47.65) 1.08 (0.68-1.73) 0.743
1298CC 22 (14.8) 13 (7.65) 2.18 (1.01-4.69) 0.046
Vahid et al., 2010 [72] Iran MTHFR C677T A1298C     MTHFR C677T        
677CC 24 (63.15) 56 (57.73) 1
677CT 11 (28.94) 37 (38.14) 0.7 (0.3-1.6) NS
677TT 3 (7.89) 4 (4.12) 1.75 (0.36-8.4) NS
MTHFR A1298C        
1298AA 12 (31.57) 39 (40.2) 1
1298AC 19 (50) 36 (37.11) 1.7 (0.7-4.0) NS
1298CC 38 CML patients (male/female: 1.05, mean age 45.0 years, SD ± 16.7) 97 healthy age- and sex-matched individuals (male/female: 0.94, mean age 44.8 years) participated in this experiment as the control group. 1.03 (0.4-3.0) NS
Hussain et al., 2012 [73] Indian MTHFR C677T     MTHFR C677T        
677CC     1
677CT     0.84 (0.36-0.94) 0.689
677TT     4.5 (1.58-12.7) 0.004
Lordelo 2011 [74];
Lordelo et al., 2012 [24]
Mixed MTHFR C677T A1298C 105 CML patients The control group consisted of 273 non-related healthy volunteers of both genders. MTHFR C677T        
677CC     0.741 (0.47-1.17) 0.193
677CT     1.130 (0.72-1.78) 0.597
677TT 43 CML patients 251 healthy controls 1.725 (0.81-3.69) 0.156
MTHFR A1298C        
1298AA     1.794 (1.14-2.83) 0.011
1298AC     0.630 (0.40-0.99) 0.047
1298CC 1 (1) 11 (4) 0.229 (0.29-1.80)  
OR (95% CI)= odds ratio (OR) with 95% confidence intervals (CI); NS= non-significant; the symbol “–” indicates data not provided.

Table 2: Association studies between methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms in CML patients and controls.

Deletion Polymorphisms in the Glutathione S-Transferases GSTM1 and GSTT1

The glutathione S-transferases (GST; EC are a family of enzymes ubiquitously distributed in nature that play a vital role in phase 2 of biotransformation, being responsible for the metabolism of a broad range of xenobiotics and carcinogens. These enzymes catalyze reactions involving the conjugation between reduced glutathione (GSH) and a variety of compounds containing an electrophilic center; most of them being xenobiotics or compounds endogenous to the organism (reactive oxygen metabolites) [126-131]. In addition to the conjugation reactions, various GST isoenzymes exhibit other GSH-dependent catalytic activities, such as reduction of organic hydroperoxides and isomerization of several unsaturated compounds, as well as non-catalytic functions related to the capture of carcinogens, intracellular transport of hydrophobic ligands, and modulation of signal transduction pathway [129]. Since xenobiotic metabolizing enzymes constitute an important line of defense against a variety of carcinogens [75], inherited differences in the capacity of these enzymes might be an important genetic factor leading to susceptibility to cancer [80].

The GSTs Mu-1 and Theta-1 are different isoforms belonging to two of the eight families or classes of the mammalian cytosolic or soluble GSTs [129,132], which appear to be primarily involved in the metabolism of foreign chemicals (xenobiotics), such as carcinogens, environmental pollutants and cancer chemotherapeutics, as well as the detoxication of potentially harmful endogenous reactive compounds (products of oxidative stress) [129]. In humans, a significant number of genetic polymorphisms among the soluble GSTs have been described [129,133]. Among them are the deletion polymorphisms (deletion of the whole gene) resulting in the lack of active enzyme in the GSTM1 (locus 1p13.3) and GSTT1 (locus 22q11.2) genes, which encode respectively the GSTs Mu-1 and Theta-1 enzymes [129,131,133136]. Although variation in GST alleles is very common in populations worldwide and will presumably make a significant contribution to individual differences (intra and inter-ethnic) [128,129], homozygous deletions in the GSTM1 or GSTT1 results in no detectable enzyme activity, and may diminish the ability to detoxify various carcinogens [24,128,131], predisposing to disease and responsiveness to therapeutic agents [133]. Therefore, occupational and environmental exposures to xenobiotics or increased oxidative stress, as well as certain hobbies and/ or lifestyle exposures may confer augmented susceptibility to CML in those individuals carrying one or both these deletions in homozygosis.

Association studies involving the deletion polymorphisms in GSTM1 and GSTT1 genes with risk of CML have been carried out in different populations. However, most of them just analyzed this risk for the null genotypes (odds ratio with 95% confidence intervals), where some results of positive association with CML risk were observed only for the GSTT1 null genotype, as shown in table 3.

Authors, year Ethnicity Polymorphisms Characteristics of cases Characteristics of controls Polymorphisms Case Control OR (95% CI) P value
Lemos et al., 1999 [75] White GSTM1 11 patients with CML, from a cohort of 160 cases with hematologic neoplasias (in cohort, 53% males, mean age 49.9 21.1 yrs) 128 healthy controls with no history of cancer or other chronic diseases, 56% females, mean age 30.8 14.2 yrs GSTM1        
Present 2(18.2) 54(42.2)
Null 9(81.8) 74(57.8) NS
Löffler et al., 2001[76] White GSTM1, GSTT1 141 patients, 55% males 150 healthy controls, 66% males GSTM1        
Present 64(45.4) 66(43.2)
Null 77 (54.6) 84 (56.8) 0.92 (0.58-1.46) 0.71
Present 110(88) 124(82.7)
Null 31 (22.0) 26 (17.3) 1.34 (0.75-2.40) 0.32
Lourenço et al., 2005 [77] Mixed GSTM1, GSTT1 125 patients (86% white), 58%
males, mean age 39.0 16.4 yrs
341 controls, 58% males, mean age 53.0 4.3 yrs, ethnicity matched GSTM1        
Present 71(56.8) 192(56.3)
Null 54(43.2) 149(43.7) 0.98 (0.65-1.50) 1
Present 102(81.6) 281(82.4)
Null 23(18.4) 60(17.6) 1.06 (0.62-1.80) 0.95
Mondal et al., 2005 [78] Indian GSTM1, GSTT1 81 patients, 70% males, median age 40 (3–81) yrs 123 healthy controls without history of cancer or other chronic diseases, 55% males, median age 35 (19–65) yrs, geographically and ethnicity matched GSTM1        
Present 58 (71.6) 89 (72.3) 1
Null 23 (28.4) 34 (27.7) 1.04 (0.55-1.93) 0.91
Present 65 (80.2) 114 (92.7)
Null 16 (19.8) 9 (7.3) 3.12 (1.3-7.45) 0.008
Hishida et al., 2005 [79] East Asian GSTM1, GSTT1 51 patients, 63% males, mean age 47.4 (21–78) yrs 476 controls, 61% males, mean age 49.7 (17–89) yrs GSTM1        
Present 25 (49.0) 227 (47.7)
Null 26 (51.0) 249 (52.3) 0.95 (0.53-1.69) 0.857
Present 22 (43.1) 238 (50.0)
Null 29 (56.9) 238 (50.0) 1.32 (0.74-2.36) 0.353
Bajpai et al., 2007 [80] Indian GSTM1, GSTT1 80 patients, 73% males, mean age 36.2 10.9 yrs 105 healthy controls, 56% males, mean age 36.8 11.3 yrs, and ethnicity matched GSTM1        
Present 56 (70%) 79 (75.2%)
Null 24 (30%) 26 (24.7%) 1.30 (0.65-2.63) 0.530
Present 64 (80%) 96 (91.4%)
      2.67 (1.03-7.01) 0.0417
Chen et al., 2008 [81] East Asian Null
16 (20%)
50 (46.3)
58 (53.7)
57 (52.8)
9 (8.5%)
91 (44.6)
113 (55.4)
104 (51.0)
      0.95 (0.59-1.53) NS
      0.91 (0.57-1.45) NS
Taspinar et al., 2008 [82] Turkish Null
100 (49.0)
59 (55,1)
51 (47.2)
75 (57,7)
Null 48 (44,9) 55 (42,3) 1.11  (0.66-1.86) 0.693
Present 64 (59,8) 105 (80,8) 1
Null 43 (40,2) 25 (19,2) 2.82  (1.58-5.05) < 0.001
Souza et al., 2008 [83] Mixed GSTM1, GSTT1 53 patients, 57% males, mean age 41.0 21 yrs 304 healthy controls, 57% females, mean age 53.0 4.3 yrs GSTM1        
Present 36(67.9) 190(62.5)
Null 17(32.1) 114(37.5) NS
Present 43(81.1) 265(87.2)
Null 10(18.9) 39(12.8) NS
Ovsepyan et al., 2010 [84] White/Russian GSTM1, GSTT1 83 patients, mean age 56.9  yrs Control group included 205
healthy unrelated volunteers. The
average age of the control patients did not significantly
differ from that in the CML patient group.
Present 39 (46.99) 111 (54.15) 0.75 (0.45-1.25) 0.33
Null 44 (53.01) 94 (45.85) 1.33 (0.80-2.22) 0.33
Present 63 (75.90) 178 (86.83) 0.48 (0.25-0.91) 0.04
Null 20 (24.10) 27 (13.17) 2.09 (1.10-3.99) 0.04
Mahmoud et al., 2010 [85] Egyptian GSTM1, GSTT1 30 patients, mean age 41.7 yrs 20 age and sex matched healthy controls. GSTM1        
Present 16(53.3) 12(60)
Null 14(46.7)) 8(40) 1.313 (0.42-4.13) 0.0642
Present 12(40) 17(85)
Null 18(60) 3(15) 8.50 (2.04-35.46) 0.002
Lordelo, 2011 [74];
Lordelo et al., 2012 [24]
Mixed GSTM1, GSTT1 105 CML patients The control group consisted of 273 non-related healthy volunteers of both genders. GSTM1        
Present 50 (47.6) 97 (35.5) 1.65 (1.05-2.60) 0.031
Null 55 (52.4) 176 (64.5) 0.61 (0.38-0.96) 0.031
Present 84 (80) 208 (76.2) 1.23 (0.70-2.13) 0.473
Null 21 (20) 65 (23.8) 0.82 (0.47-1.42) 0.473
Özten et al., 2012 [86] White / Turkish GSTM1, GSTT1 106 patients, 56.6% males, mean age 35.1   yrs The control group consisted of 190 healthy unrelated volunteers without history of cancer or other chronic diseases 56.3% males, mean age 38.3  yrs GSTM1        
Present 58 (54.7) 109 (57.4) 1
Null 48 (45.3) 81 (42.6) 1.11 (0.69, 1.80) 0.714
Present 59 (55.7) 155 (81.6) 1
Null 47 (44.3) 35 (18.4) 3.53 (2.08, 6.00) < 0.0001
Bhat et al., 2012 [87] Indian GSTM1, GSTT1 75 CML patients (43 males and 32 females; age (mean ± S.D) 42.3 ± 13.4 years) 124 unrelated non-malignant controls (76 male and 48 females; age (mean ± S.D) 41.5 ± 12.9) GSTM1        
Present 44 (59%) 81(65%) 1
Null 31 (41%) 43 (35%) 1.32 (0.73 - 2.40) 0.4295
Present 48 (64%) 98 (79%) 1
Null 27 (36%) 26 (21%) 2.12 (1.12 - 4.02) 0.0308
OR (95% CI)= odds ratio (OR) with 95% confidence intervals (CI); NS= non-significant (p-values not provided); the symbol “–” indicates data not provided.

Table 3: Association studies among the deletion polymorphisms in the glutathione S-transferases GSTM1 and GSTT1 in CML patients and controls.

However, one of the two articles that analyzed both genotypes of the deletion polymorphisms (null and non-null genotypes) in GSTM1 and GSTT1 genes found a positive association between CML risk with GSTM1 non-null genotype (OR = 1.649; 95% CI = 1.05-2.6), while GSTM1 null genotype decreased this risk (OR = 0.606; 95% CI = 0.21- 0.77) [24]. Although it is unbelievable that the presence of an enzyme, which operates in carcinogen detoxification, could increase CML risk, in several instances GST activity does not result in the detoxification of xenobiotics and may even lead to a more reactive compound than the parental one. Additionally, incomplete detoxification by GST may occur with certain esters, ethers, and organic phosphates, and the unconjugated cleavage product still provides a chemical threat to the cell. Moreover, while toxification by GST is undesirable in normal circumstances, it can be exploited in cancer chemotherapy to treat tumors that overexpress GST [127]. Thus, these effects need to be further investigated. Also, the GSTM1 gene demonstrates polymorphisms that arise from homo and heterozygotic combinations of the GSTM1*0, GSTM1*A and GSTM1*B alleles [133,136], and although it is believed that GSTM1*A and GSTM1*B alleles encode proteins that are catalytically identical [130,133], a linkage disequilibrium between GSTM1 and GSTM3 (both at locus 1p13.3) has been reported, and this may alter the expression of these class Mu transferases. For example, it has been demonstrated that subjects with GSTM1*A/GSTM3*B should express GSTM3 at higher levels than those with GSTM1*0/GSTM3*A or GSTM1*B/GSTM3*A [133], and this needs to better investigated, at least for those subjects that are less responsive or non-responsive to therapeutic agents.

Still considering possible genetic interactions, for the most part, polymorphisms in individual GST genes do not confer a markedly increased risk of cancer, but combinations of the GST M1 and T1 alleles taken together or with alleles of other genes encoding for detoxification or antioxidant enzymes are likely to have an additive effect in conferring predisposition to cancer or to influence responsiveness to chemotherapeutic agents in its treatment [129]. Thus, some of the association studies showed in table 3 also evaluated interactions among the deletion polymorphisms in the GSTM1 and GSTT1 genes with other gene polymorphisms related to xenobiotic metabolizing enzyme of phases I (eg. cytochrome P450s – CYPs or P450s) and/or II (eg. N-acetyltransferase 2 - NAT2; NAD(P)H:quinone oxidoreductase 1 - NQO1) in the CML risk [75,76,79,8183,86]. However, results of association with increased CML risk were only found for the interactions between GSTM1normal/GSTT1null and/or GSTM1null/GSTT1null genotypes [82,83,86], although it has been proposed that this risk would be modulated little by GSTT1 and GSTM1 deletions [79]. These results suggested an interaction between GSTT1 and GSTM1 genotypes and that GSTT1 null genotype could be the significant risk factor for CML [82]. Nevertheless, as previously mentioned, associations between GSTT1 null genotype and increased CML risk were not found in many studies [24,77,79,81]. Besides the small sample size of some studies resulting in very broad confidence intervals, such contrary findings may also reflect geographical differences in the type of environmental carcinogens to which different populations are exposed [75]. They also may reflect differences in CML risk among the different ethnic groups, since inter- and intra-ethnic differences in the allele frequencies of GSTM1 and GSTT1 null genotypes have been documented worldwide [128]. Thus, studies dealing with a large population in several ethnicities should be encouraged to better understand the biological significance of these polymorphisms in CML susceptibility in each ethnic group, as well as in understanding their role in the variability of the disease course and in responsiveness to therapeutic agents, mainly for women <50 years, where analysis of survival carried out from the SEER database suggested possible higher rates of TKI resistance for the African-American group [10].

Haptoglobin Polymorphism

Although BCR-ABL transcripts are known to be associated uniquely with acute and chronic leukemia, studies using sensitive techniques of reverse transcriptase-polymerase chain reaction (RTPCR) have detected small amounts of such transcripts in leukocytes of normal healthy adults [137,138] and children [137], as well as in human hematopoietic non-CML cell lines [138]. This suggests that such forms of illegitimate genetic recombination may occur regularly in hematopoietic precursors and in cultured cell lines as a consequence of an inherent basal level of genomic instability [138]. However, only infrequently do the cells acquire the capacity to produce leukemia in humans. Although success in producing a leukemic phenotype depends on the fusion gene structure producing a functional protein and also the occurrence of chromosomal translocation in a relatively early precursor cell with self-renewal capacity, which were not detected in several normal leukocytes and in the non-CML cell lines [138], it is also possible that these transcripts represent “errors” that occur because of the close proximity of BCR and ABL1 genes during the late S-phase (S to G2 transition) of the cell cycle, and that immune surveillance prevents the emergence of CML in individuals who remain healthy [20,139]. Therefore, the possible association of leukemia with haptoglobin (Hp), an acute-phase plasma α2-glycoprotein with several functional properties, including antioxidant, anti-inflammatory and immunomodulatory ones, was first suggested by Latner and Zaki [88,93,140].

The main biological function of Hp is binding free hemoglobin, removing it from the circulation and limiting hemolysis and iron loss during normal erythrocyte turnover, thereby preventing oxidative damage mediated by excess iron in the circulation. As a result, Hp functions as an antioxidant [98,141,142]. In addition, Hp has the ability to regulate immune cell responses and host immunity, modulating the balance of helper T-cell types 1 and 2 (Th1/Th2) within the body, and thus supporting proliferation and functional differentiation of B and T cells as part of homeostasis and in response to antigen stimulation [141143]. Because of its immunomodulatory property, Hp may inhibit or stimulate the immune response, and its concentration in malignancies and in inflammatory and infectious processes is elevated [142]. However, Hp of humans is polymorphic, and its serum levels are phenotype-dependent [144,145], as is its ability to block hemoglobininduced oxidative stress and damage and its anti-inflammatory activity [24,141,143,145-147]. Thus, many clinical studies have demonstrated a link between Hp polymorphism and a broad range of pathological conditions, often with divergent clinical consequences, and such associations probably reflect functional differences among the phenotypes [141,145-148].

The human Hp gene is located on chromosome 16 (locus 16q22.1) and its molecular variation was described by Smithies [149] , who identified by starch gel electrophoresis three major phenotypes, Hp1-1, Hp2-1, and Hp2-2, which are controlled by two autosomal codominant alleles, Hp*1 and Hp*2. After that, on starch gels with urea, the Hp*1 allele revealed two subtypes, Hp*1S and Hp*1F, and then the three common types of Hp could be subdivided into a total of six, which are products of expression of the combination of the alleles Hp*1F, Hp*1S and Hp*2 [142,145,147,149,150].

In view of the above explanations and also that: (1) Hp binds to different immunologic cells by specific receptors, and among them are the natural killer (NK) cells [141], an important part of immune surveillance [151]; (2) the three main Hp phenotypes have the same binding affinities for hemoglobin [143], but Hp2-2 removes iron to the extravascular space more slowly because it is a larger molecule [133]; so, the antioxidant capacity of the Hp 1-1 phenotype is higher than Hp 2-2 because free hemoglobin remains in the circulation longer and causes greater oxidative stress [142,144,152]; (3) ALL, AML, and CML have been associated with an increased incidence of Hp 1-1, but the explanation of this phenomenon is difficult [93]; and finally (4) genome-wide analysis of gene-expression profiles in CML cells using a cDNA microarray has shown haptoglobin (HP1) to be one of the upregulated elements [153]; these apparently divergent data can only be understood through additional characterization of the Hp*1 subtype polymorphisms (Hp*1S and Hp*1F). However, only one study carried by Lordelo et al. which worked with a mixed population (Brazilian), researched a possible association of CML with these Hp*1 subtype polymorphisms [24] in a case control study, as can be seen in table 4. Even though no association was found in this work between a particular Hp genotype when considering the whole population, significant results were obtained for individuals of black skin color, where Hp1F- 1S individuals presented an increased risk (OR = 7.200; 95% CI = 0.94- 54.94; p = 0.037), while Hp1S-2 individuals, a decreased risk (OR = 0.619; 95% CI = 0.44-0.87; p = 0.011) [24].

Authors, year Ethnicity Polymorphisms Characteristics of cases Characteristics of controls Types/ Subtypes Case
Control (N/%) OR (95% CI) P value
Latner and Zaki, 1960 [88] White (England) Haptoglobin 10 adult patients with CML 30 normal individuals 1-1 4(40) 3(10)
2-1 4(40) 15(50)
2-2 2(20) 12(40)
Peacock, 1966 [89] White Haptoglobin 24 adult patients with CML 101 patients with a variety of disease, not including leukemia. 1-1 4(16.7) 15(14.8)
2-1 6 (25) 33(32.7)
2-2 14(58.3) 53(52.5)
*Baxi and Camoens, 1969 [90];
Blake et al., 1971 [91];
Naik et al., 1979 [92]
India Haptoglobin  85 adult patients with CML 1205 normal controls for the study by Naik et al., 1979, which were not provided by authors. Blake et al. 1971, Hp types in nine population groups from India. Baxi and Camoens, 1969, normal control from north and western India 1-1 5(5.9) 36(2.98)
2-1 23(27.05) 458(38)
2-2 57(67.05) 1025(85)
*Fröhlander, 1984 [94] Sweden Haptoglobin 22 adult patients with CML 2297 normal controls 1-1 4(18.2) 311(13.5)
2-1 8(36.4) 1091(47.5)
2-2 10(45.4) 895(39)
Michell et al., 1988 [95]   Haptoglobin 22 adult patients with CML 361 blood donors 1-1 5(22.7) 56(15.5)
2-1 10(45.5) 175(48.5)
2-2 6(27.3) 124(34.3)
Campregher et al., 2004 [96] Mixed Haptoglobin 78 adult patients with CML 210 blood donors from the same geographical region 1-1 13(16.7) 45(22.9)
2-1 42(53.8) 108(54.8)
2-2 23(29.5) 44(22.3)
Lordelo, 2011 [74];
Lordelo et al., 2012 [24]
Mixed Haptoglobin 105 CML patients 273 non-related healthy volunteers of both genders 1F-1F 4(3.81) 16(5.9) 0.636 (0.208-1.949) 0.425
1F-1S 12(11.43) 18(6.6) 1.828 (0.848-3.940) 0.119
1S-1S 5(4.76) 28(10.3) 0.438 (0.164-1.165) 0.090
1F-2 13(12.38) 36(13.2) 0.930 (0.472-1.833) 0.835
1S-2 32(30.48) 93(34.1) 0.848 (0.522-1.378) 0.506
2-2 39(37.14) 82(30) 1.376 (0.858-2.209) 0.185
OR (95% CI) = odds ratio (OR) with 95% confidence intervals (CI); NS = non-significant; the symbol “–” indicates data not provided. *Data were collected from Nevo and Tatarsky 1986 [93] (the controls were added).

Table 4: Association studies among haptoglobin types and subtypes in CML patients and controls.

While Hp*1 and Hp*2 alleles have always been found in every population examined to date, there is a significant difference in their distribution in populations worldwide, as well as in the distribution of the Hp*1F and Hp*1S allele frequencies [146,147], which suggests that particular populations are susceptible to particular diseases [146]. Moreover, even though the Hp*1F allele is rarer than the Hp*1S allele, the higher frequencies of the Hp*1 allele in South America and Africa seems to be linked to a higher Hp*1F frequency in studies that make such data available [146,147].

Thus, to avoid spurious associations and especially loss of some important association, Hp*1 subtypes cannot be treated as a single block of Hp 1-1 phenotypes in association studies, particularly those involving South America, Africa or admixed populations. This has already been indicated in other studies carried out with Brazilian athletes, which verified differences in the biological responses among Hp*1 alleles, particularly those involving oxidative stress [154,155]. Therefore, studies evaluating a possible association between Hp subtypes and those leukemia associated with an increased incidence of Hp 1-1 (CML, ALL and AML) should be encouraged in several ethnicities, particularly in South America and Africa, where Hp*1F allele frequency is higher. These studies are particularly important after the findings of Mandal et al. [10], where, as previously mentioned, the survival rates of African-American men <50 years with CML was significantly lower compared to those of Caucasians in the pre-TKI era, while the same age group of African-American women had lower relative survival rates also compared to Caucasian women in the post- TKI era [10].


Since little is known about individual susceptibility to CML, and the mechanisms behind disease progression are not fully understood, the MTHFR, GSTM1, GSTT1 and Hp polymorphisms are good candidates for a possible genetic susceptibility to the induction of the Ph chromosome and the emergence of CML. However, since these polymorphisms vary among ethnic groups, and populations worldwide vary considerably in their predisposition to diseases and in the allele frequencies of pharmacogenetically important loci, studies in several ethnicities are required to better understand the biological significance of these polymorphisms in CML susceptibility, as well as in understanding the variability of the disease course and the patients’ response to medication. As it has been demonstrated that there are differences in the incidence and death rates of CML by gender and race/ ethnicity pre- and post-TKI, and various association studies focusing the addressed polymorphisms analyzed relatively small groups of patients and controls which resulted in very broad intervals of statistical confidence of relative risks, studies with large populations worldwide are required to remedy these methodological problems and to confirm the role of MTHFR, GSTM1, GSTT1 and Hp polymorphisms in CML.


  1. Faderl S, Talpaz M, Estrov Z, O'Brien S, Kurzrock R, et al. (1999) The biology of chronic myeloid leukemia. N Engl J Med 341: 164-172.
  2. Piller G (2001) Leukaemia - a brief historical review from ancient times to 1950. Br J Haematol 112: 282-292.
  3. Quintás-Cardama A, Cortes JE (2006) Chronic myeloid leukemia: diagnosis and treatment. Mayo Clin Proc 81: 973-988.
  4. Van Etten RA (2012) Cellular and molecular biology of chronic myeloid leukemia.
  5. Jabbour E, Cortes JE, Giles FJ, O'Brien S, Kantarjian HM (2007) Current and emerging treatment options in chronic myeloid leukemia. Cancer 109: 2171-2181.
  6. Jabbour E, Kantarjian H (2012) Chronic myeloid leukemia: 2012 update on diagnosis, monitoring, and management. Am J Hematol 87: 1037-1045.
  7. Bortolheiro TC, Chiattone CS (2008) Chronic Myeloide Leukemia: natural history and classification. Rev Bras Hematol Hemoter 30(Supl. 1): 3-7.
  8. Greer J, Foerster J, Lukens JN, Rodgers GM, Paraskevas F, et al. (2004) Wintrobe’s Clinical Hematology Vol. 2. (11th ed.), Lippicott Williams & Wilkins, Philadelphia/USA.
  9. Kurzrock R, Kantarjian H, Talpaz M (2001) Chronic myelogenous leukemia in chronic phase. Curr Treat Options Oncol 2: 245-252.
  10. Mandal R, Bolt DM, Shah BK (2012) Disparities in chronic myeloid leukemia survival by age, gender, and ethnicity in pre- and post-imatinib eras in the US. Acta Oncol.
  11. Calabretta B, Perrotti D (2004) The biology of CML blast crisis. Blood 103: 4010-4022.
  12. Stenehjim D, Albright F (2012) Creation of a chronic myeloid leukemia retrospective outcomes research registry.
  13. Surveillance Epidemiology and End Results (SEER) Stat Fact Sheets: Chronic Myeloid Leukemia.
  14. Hochhaus A (2011) Educational session: managing chronic myeloid leukemia as a chronic disease. Hematology Am Soc Hematol Educ Program 2011: 128-135.
  15. Ahmad R, Tripathi AK, Tripathi P, Singh R, Singh S, et al. (2008) Oxidative stress and antioxidant status in patients with chronic myeloid leukemia. Indian J Clin Biochem 23: 328-333.
  16. Cortes J (2004) Natural history and staging of chronic myelogenous leukemia. Hematol Oncol Clin North Am 18: 569-584, viii.
  17. Nowell PC, Hungerford DA (1960) A minute chromosome in human chronic granulocytic leukemia. Science 142: 1497.
  18. Saglio G, Morotti A, Mattioli G, Messa E, Giugliano E, et al. (2004) Rational approaches to the design of therapeutics targeting molecular markers: the case of chronic myelogenous leukemia. Ann N Y Acad Sci 1028: 423-431.
  19. Rowley JD (1973) Letter: A new consistent chromosomal abnormality in chronic myelogenous leukaemia identified by quinacrine fluorescence and Giemsa staining. Nature 243: 290-293.
  20. Laurent E, Talpaz M, Kantarjian H, Kurzrock R (2001) The BCR gene and philadelphia chromosome-positive leukemogenesis. Cancer Res 61: 2343-2355.
  21. Chen Z (2006) Molecular cytogenetic markers related to prognosis in hematological malignancies. World J Pediatr 4: 252-259.
  22. Nowicki MO, Falinski R, Koptyra M, Slupianek A, Stoklosa T, et al. (2004) BCR/ABL oncogenic kinase promotes unfaithful repair of the reactive oxygen species-dependent DNA double-strand breaks. Blood 104: 3746-3753.
  23. Kim DH, Xu W, Ma C, Liu X, Siminovitch K, et al. (2009) Genetic variants in the candidate genes of the apoptosis pathway and susceptibility to chronic myeloid leukemia. Blood 113: 2517-2525.
  24. Lordelo GS, Miranda-Vilela AL, Akimoto AK, Alves PC, Hiragi CO, et al. (2012) Association between methylene tetrahydrofolate reductase and glutathione S-transferase M1 gene polymorphisms and chronic myeloid leukemia in a Brazilian population. Genet Mol Res 11: 1013-1026.
  25. Katsuki K, Shinohara K, Takeda K, Ariyoshi K, Yamada T, et al. (2000) Chronic neutrophilic leukemia with acute myeloblastic transformation. Jpn J Clin Oncol 30: 362-365.
  26. Pérez-Caro M, Sánchez-García I (2007) BCR-ABL and Human Cancer. In: Srivastava R (Editor). Apoptosis, Cell Signaling, and Human Diseases: Molecular Mechanisms, Volume 1. Humana Press Inc., Totowa, New Jersey, United States. pp 3-33. (384 pages).
  27. Heisterkamp N, Stam K, Groffen J, de Klein A, Grosveld G (1985) Structural organization of the bcr gene and its role in the Ph' translocation. Nature 315: 758-761.
  28. Mondal BC, Majumdar S, Dasgupta UB, Chaudhuri U, Chakrabarti P, et al. (2006) e19a2 BCR-ABL fusion transcript in typical chronic myeloid leukaemia: a report of two cases. J Clin Pathol 59: 1102-1103.
  29. Jinawath N, Norris-Kirby A, Smith BD, Gocke CD, Batista DA, et al. (2009) A rare e14a3 (b3a3) BCR-ABL fusion transcript in chronic myeloid leukemia: diagnostic challenges in clinical laboratory practice. J Mol Diagn 11: 359-363.
  30. Dhahi MAR, Mohaymen NA, Murad NS (2010) Detection of BCR-ABL protein in chronic myeloid leukemia patients using Immunocytochemistry. Iraqi J Med Sci 8: 39-43.
  31. Li S, Ilaria RL Jr, Million RP, Daley GQ, Van Etten RA (1999) The P190, P210, and P230 forms of the BCR/ABL oncogene induce a similar chronic myeloid leukemia-like syndrome in mice but have different lymphoid leukemogenic activity. J Exp Med 189: 1399-1412.
  32. Kantarjian HM, Talpaz M, Dhingra K, Estey E, Keating MJ, et al. (1991) Significance of the P210 versus P190 molecular abnormalities in adults with Philadelphia chromosome-positive acute leukemia. Blood 78: 2411-2418.
  33. Score J, Calasanz MJ, Ottman O, Pane F, Yeh RF, et al. (2010) Analysis of genomic breakpoints in p190 and p210 BCR-ABL indicate distinct mechanisms of formation. Leukemia 24: 1742-1750.
  34. Arana-Trejo RM, Ruíz Sánchez E, Ignacio-Ibarra G, Báez de la Fuente E, Garces O, et al. (2002) BCR/ABL p210, p190 and p230 fusion genes in 250 Mexican patients with chronic myeloid leukaemia (CML). Clin Lab Haematol 24: 145-150.
  35. Carvalho PVB, Lourenço GJ, Zocca M, Pagnano KBB, Lorand-Metze I, et al. (2003) Expression of p190 BCR-ABL fusion gene in a patient with chronic myeloid leukemia. Rev Bras Hematol Hemoter 25:173-176.
  36. Verma D, Kantarjian HM, Jones D, Luthra R, Borthakur G, et al. (2009) Chronic myeloid leukemia (CML) with P190 BCR-ABL: analysis of characteristics, outcomes, and prognostic significance. Blood 114: 2232-2235.
  37. Kantarjian HM, Dixon D, Keating MJ, Talpaz M, Walters RS, et al. (1988) Characteristics of accelerated disease in chronic myelogenous leukemia. Cancer 61: 1441-1446.
  38. Kadam PR, Nanjangud GJ, Advani SH, Nair C, Banavali S, et al. (1991) Chromosomal characteristics of chronic and blastic phase of chronic myeloid leukemia. A study of 100 patients in India. Cancer Genet Cytogenet 51: 167-181.
  39. Johansson B, Fioretos T, Mitelman F (2002) Cytogenetic and molecular genetic evolution of chronic myeloid leukemia. Acta Haematol 107: 76-94.
  40. Williams RT, Sherr CJ (2008) BCR-ABL and CDKN2A: a dropped connection. Nat Rev Cancer 8: 563.
  41. Martinelli G, Iacobucci I, Papayannidis C, Soverini S (2009) New targets for Ph+ leukaemia therapy. Best Pract Res Clin Haematol 22: 445-454.
  42. Dovat S (2011) Ikaros in hematopoiesis and leukemia. World J Biol Chem 2: 105-107.
  43. Sirvent A, Benistant C, Roche S (2008) Cytoplasmic signalling by the c-Abl tyrosine kinase in normal and cancer cells. Biol Cell 100: 617-631.
  44. Pendergast AM (2002) The Abl family kinases: mechanisms of regulation and signaling. Adv Cancer Res 85: 51-100.
  45. Hantschel O, Superti-Furga G (2004) Regulation of the c-Abl and Bcr-Abl tyrosine kinases. Nat Rev Mol Cell Biol 5: 33-44.
  46. Maru Y, Witte ON (1991) The BCR gene encodes a novel serine/threonine kinase activity within a single exon. Cell 67: 459-468.
  47. Ridley AJ (2004) Rho proteins and cancer. Breast Cancer Res Treat 84: 13-19.
  48. Takeda N, Shibuya M, Maru Y (1999) The BCR-ABL oncoprotein potentially interacts with the xeroderma pigmentosum group B protein. Proc Natl Acad Sci U S A 96: 203-207.
  49. Diekmann D, Brill S, Garrett MD, Totty N, Hsuan J, et al. (1991) Bcr encodes a GTPase-activating protein for p21rac. Nature 351: 400-402.
  50. Pendergast AM, Muller AJ, Havlik MH, Maru Y, Witte ON (1991) BCR sequences essential for transformation by the BCR-ABL oncogene bind to the ABL SH2 regulatory domain in a non-phosphotyrosine-dependent manner. Cell 66: 161-171.
  51. Skorski T, Nieborowska-Skorska M, Szczylik C, Kanakaraj P, Perrotti D, et al. (1995) C-RAF-1 serine/threonine kinase is required in BCR/ABL-dependent and normal hematopoiesis. Cancer Res 55: 2275-2278.
  52. Sattler M, Salgia R (1997) Activation of hematopoietic growth factor signal transduction pathways by the human oncogene BCR/ABL. Cytokine Growth Factor Rev 8: 63-79.
  53. Cortez D, Reuther G, Pendergast AM (1997) The Bcr-Abl tyrosine kinase activates mitogenic signaling pathways and stimulates G1-to-S phase transition in hematopoietic cells. Oncogene 15: 2333-2342.
  54. Cortez D, Stoica G, Pierce JH, Pendergast AM (1996) The BCR-ABL tyrosine kinase inhibits apoptosis by activating a Ras-dependent signaling pathway. Oncogene 13: 2589-2594.
  55. Andrade GV (2008) Papel da P190BCR-ABL como parâmetro de recaída na leucemia mielóide crônica. Rev Bras Hematol Hemoter 30: 297-302.
  56. Gluzman D, Imamura N, Sklyarenko L, Nadgornaya V, Zavelevich M, et al. (2005) Malignant diseases of hematopoietic and lymphoid tissues in Chernobyl clean-up workers. Hematol J 5: 565-571.
  57. Rinsky RA (1989) Benzene and leukemia: an epidemiologic risk assessment. Environ Health Perspect 82: 189-191.
  58. Ciccone G, Mirabelli D, Levis A, Gavarotti P, Rege-Cambrin G, et al. (1993) Myeloid leukemias and myelodysplastic syndromes: chemical exposure, histologic subtype and cytogenetics in a case-control study. Cancer Genet Cytogenet 68: 135-139.
  59. Van Maele-Fabry G, Duhayon S, Lison D (2007) A systematic review of myeloid leukemias and occupational pesticide exposure. Cancer Causes Control 18: 457-478.
  60. Zahm SH, Ward MH (1998) Pesticides and childhood cancer. Environ Health Perspect 106: 893-908.
  61. Bassil KL, Vakil C, Sanborn M, Cole DC, Kaur JS, et al. (2007) Cancer health effects of pesticides. Can Fam Physician 53: 1704-1711.
  62. Hole PS, Darley RL, Tonks A (2011) Do reactive oxygen species play a role in myeloid leukemias? Blood 117: 5816-5826.
  63. Sattler M, Verma S, Shrikhande G, Byrne CH, Pride YB, et al. (2000) The BCR/ABL tyrosine kinase induces production of reactive oxygen species in hematopoietic cells. J Biol Chem 275: 24273-24278.
  64. Nieborowska-Skorska M, Kopinski PK, Ray R, Hoser G, Ngaba D, et al. (2012) Rac2-MRC-cIII-generated ROS cause genomic instability in chronic myeloid leukemia stem cells and primitive progenitors. Blood 119: 4253-4263.
  65. Robien K, Ulrich CM, Bigler J, Yasui Y, Gooley T, et al. (2004) Methylenetetrahydrofolate reductase genotype affects risk of relapse after hematopoietic cell transplantation for chronic myelogenous leukemia. Clin Cancer Res 10: 7592-7598.
  66. Hur M, Park JY, Cho HC, Lee KM, Shin HY, et al. (2006) Methylenetetrahydrofolate reductase A1298C genotypes are associated with the risks of acute lymphoblastic leukaemia and chronic myelogenous leukaemia in the Korean population. Clin Lab Haematol 28: 154-159.
  67. Moon HW, Kim TY, Oh BR, Min HC, Cho HI, et al. (2007) MTHFR 677CC/1298CC genotypes are highly associated with chronic myelogenous leukemia: a case-control study in Korea. Leuk Res 31: 1213-1217.
  68. Barbosa CG, Souza CL, Moura Neto JP, Arruda MGB, Barreto JH, et al. (2008) Methylenetetrahydrofolate reductase polymorphisms in myeloid leukemia patients from Northeastern Brazil. Genet Mol Biol 31: 29-32.
  69. Kim HN, Kim YK, Lee IK, Yang DH, Lee JJ, et al. (2009) Association between polymorphisms of folate-metabolizing enzymes and hematological malignancies. Leuk Res 33: 82-87.
  70. Ismail SI, Ababneh NA, Awidi A (2009) Methylenetetrahydrofolate Reductase (MTHFR) genotype association with the risk of Chronic Myelogenous Leukemia. J Med J 43: 8-14.
  71. Vahid P, Farnaz R, Zaker F, Farzaneh A, Parisa R (2010) Methylenetetrahydrofolate Reductase gene polymorphisms and risk of Myeloid Leukemia. Lab Med 41: 490-494.
  72. Hussain SR, Naqvi H, Raza ST, Ahmed F, Babu SG, et al. (2012) Methylenetetrahydrofolate reductase C677T genetic polymorphisms and risk of leukaemia among the North Indian population. Cancer Epidemiol 36: e227-231.
  73. Lordelo GS (2011) Polimorfismo nos genes MTHFR, Glutationa S-transferase (GST) e Haptoglobina (HP) e sua relação na ocorrência da Leucemia Mielóide Crônica (LMC). University of Brasilia/Brazil.
  74. Lemos MC, Cabrita FJ, Silva HA, Vivan M, Plácido F, et al. (1999) Genetic polymorphism of CYP2D6, GSTM1 and NAT2 and susceptibility to haematological neoplasias. Carcinogenesis 20: 1225-1229.
  75. Loffler H, Bergmann J, Hochhaus A, Hehlmann R, Krämer A, et al. (2001) Reduced risk for chronic myelogenous leukemia in individuals with the cytochrome P-450 gene polymorphism CYP1A1*2A. Blood 98: 3874-3875.
  76. Lourenco GJ, Ortega MM, Nascimento H, Teori MT, De Souza CA, et al. (2005) Polymorphisms of glutathione S-transferase mu1 (GSTM1) and theta 1 (GSTT1) genes in chronic myeloid leukaemia. Eur J Haematol 75: 530-531.
  77. Mondal BC, Paria N, Majumdar S, Chandra S, Mukhopadhyay A, et al. (2005) Glutathione S-transferase M1 and T1 null genotype frequency in chronic myeloid leukaemia. Eur J Cancer Prev 14: 281-284.
  78. Hishida A, Terakura S, Emi N, Yamamoto K, Murata M, et al. (2005) GSTT1 and GSTM1 deletions, NQO1 C609T polymorphism and risk of chronic myelogenous leukemia in Japanese. Asian Pac J Cancer Prev 6: 251-255.
  79. Bajpai P, Tripathi AK, Agrawal D (2007) Increased frequencies of glutathione-S-transferase (GSTM1 and GSTT1) null genotypes in Indian patients with chronic myeloid leukemia. Leuk Res 31: 1359-1363.
  80. Chen HC, Hu WX, Liu QX, Li WK, Chen FZ, et al. (2008) Genetic polymorphisms of metabolic enzymes CYP1A1, CYP2D6, GSTM1 and GSTT1 and leukemia susceptibility. Eur J Cancer Prev 17: 251-258.
  81. Taspinar M, Aydos SE, Comez O, Elhan AH, Karabulut HG, et al. (2008) CYP1A1, GST gene polymorphisms and risk of chronic myeloid leukemia. Swiss Med Wkly 138: 12-17.
  82. Souza CL, Barbosa CG, Moura Neto JP, Barreto JH, Reis MG, et al. (2008) Polymorphisms in the glutathione S-transferase theta and mu genes and susceptibility to myeloid leukemia in Brazilian patients. Genet Mol Biol 31: 39-41.
  83. Ovsepian VA, Vinogradova EIu, Sherstneva ES (2010) Cytochrome P4501A1, glutathione S-transferase M1 and T1 gene polymorphisms in chronic myeloid leukemia. Genetika 46: 1360-1362.
  84. Mahmoud S, Labib DA, Khalifa RH, Khalil REA, Marie MA (2010) CYPA1, GSTM1 and GSTT1 genetic polymorphism in Egyptian chronic myeloid leukemia patients. Res J Immunol 3: 12-21.
  85. Ozten N, Sunguroglu A, Bosland MC (2012) Variations in glutathione-S-transferase genes influence risk of chronic myeloid leukemia. Hematol Oncol 30: 150-155.
  86. Bhat G, Bhat A, Wani A, Sadiq N, Jeelani S, et al. (2012) Polymorphic variation in glutathione-S-transferase genes and risk of chronic myeloid leukaemia in the Kashmiri population. Asian Pac J Cancer Prev 13: 69-73.
  87. LATNER AL, ZAKI AH (1960) Clinical uses of starch gel electrophoresis with special reference to leukaemia. Clin Chim Acta 5: 22-25.
  88. Peacock AC (1966) Serum haptoglobin type and leukemia: an association with possible etiological significance. J Natl Cancer Inst 36: 631-639.
  89. Baxi AJ, Camoens H (1969) Studies on haptoglobin types in various Indian populations. Hum Hered 19: 65-70.
  90. Blake NM, Kirk RL, McDermid EM, Omoto K, Ahuja YR (1971) The distribution of serum protein and enzyme group systems among North Indians. Hum Hered 21: 440-457.
  91. Naik SN, Ishwad CS, Nadkarni JS, Nadkarni JJ, Advani SH (1979) Study of haptoglobin polymorphism and its significance in human leukemias. Eur J Cancer 15: 1463-1469.
  92. Nevo S, Tatarsky I (1986) Serum haptoglobin types and leukemia. Hum Genet 73: 240-244.
  93. Fröhlander N (1984) Haptoglobin groups and leukemia. Hum Hered 34: 311-313.
  94. Mitchell RJ, Carzino R, Janardhana V (1988) Associations between the two serum proteins haptoglobin and transferrin and leukaemia. Hum Hered 38: 144-150.
  95. Campregher PV, Lorand-Metze I, Grotto HZW, Sonati MF (2004) Haptoglobin phenotypes in Brazilian patients with Leukemia. J Bras Patol Med Lab 40: 307-309.
  96. Friso S, Choi SW, Girelli D, Mason JB, Dolnikowski GG, et al. (2002) A common mutation in the 5,10-methylenetetrahydrofolate reductase gene affects genomic DNA methylation through an interaction with folate status. Proc Natl Acad Sci U S A 99: 5606-5611.
  97. Miranda-Vilela AL (2012) Role of polymorphisms in factor V (FV Leiden), prothrombin, plasminogen activator inhibitor type-1 (PAI-1), methylenetetrahydrofolate reductase (MTHFR) and Cystathionine ß-synthase (CBS) genes as risk factors for thrombophilias. Mini Rev Med Chem 12: 997-1006.
  98. Qu GZ, Grundy PE, Narayan A, Ehrlich M (1999) Frequent hypomethylation in Wilms tumors of pericentromeric DNA in chromosomes 1 and 16. Cancer Genet Cytogenet 109: 34-39.
  99. Lengauer C, Kinzler KW, Vogelstein B (1997) DNA methylation and genetic instability in colorectal cancer cells. Proc Natl Acad Sci U S A 94: 2545-2550.
  100. Sinthuwiwat T, Poowasanpetch P, Wongngamrungroj A, Soonklang K, Promso S, et al. (2012) Association of MTHFR polymorphisms and chromosomal abnormalities in leukemia. Dis Markers 32: 115-121.
  101. Blount BC, Mack MM, Wehr CM, MacGregor JT, Hiatt RA, et al. (1997) Folate deficiency causes uracil misincorporation into human DNA and chromosome breakage: implications for cancer and neuronal damage. Proc Natl Acad Sci U S A 94: 3290-3295.
  102. Duthie SJ, Narayanan S, Brand GM, Pirie L, Grant G (2002) Impact of folate deficiency on DNA stability. J Nutr 132: 2444S-2449S.
  103. Wiemels JL, Smith RN, Taylor GM, Eden OB, Alexander FE, et al. (2001) Methylenetetrahydrofolate reductase (MTHFR) polymorphisms and risk of molecularly defined subtypes of childhood acute leukemia. Proc Natl Acad Sci U S A 98: 4004-4009.
  104. Ulrich CM, Yasui Y, Storb R, Schubert MM, Wagner JL, et al. (2001) Pharmacogenetics of methotrexate: toxicity among marrow transplantation patients varies with the methylenetetrahydrofolate reductase C677T polymorphism. Blood 98: 231-234.
  105. Ma J, Stampfer MJ, Giovannucci E, Artigas C, Hunter DJ, et al. (1997) Methylenetetrahydrofolate reductase polymorphism, dietary interactions, and risk of colorectal cancer. Cancer Res 57: 1098-1102.
  106. Goyette P, Pai A, Milos R, Frosst P, Tran P, et al. (1998) Gene structure of human and mouse methylenetetrahydrofolate reductase (MTHFR). Mamm Genome 9: 652-656.
  107. Robien K, Ulrich CM (2003) 5,10-Methylenetetrahydrofolate reductase polymorphisms and leukemia risk: a HuGE minireview. Am J Epidemiol 157: 571-582.
  108. Frosst P, Blom HJ, Milos R, Goyette P, Sheppard CA, et al. (1995) A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet 10: 111-113.
  109. van der Put NM, Gabreëls F, Stevens EM, Smeitink JA, Trijbels FJ, et al. (1998) A second common mutation in the methylenetetrahydrofolate reductase gene: an additional risk factor for neural-tube defects? Am J Hum Genet 62: 1044-1051.
  110. James SJ, Pogribna M, Pogribny IP, Melnyk S, Hine RJ, et al. (1999) Abnormal folate metabolism and mutation in the methylenetetrahydrofolate reductase gene may be maternal risk factors for Down syndrome. Am J Clin Nutr 70: 495-501.
  111. Hobbs CA, Sherman SL, Yi P, Hopkins SE, Torfs CP, et al. (2000) Polymorphisms in genes involved in folate metabolism as maternal risk factors for Down syndrome. Am J Hum Genet 67: 623-630.
  112. Hassold TJ, Burrage LC, Chan ER, Judis LM, Schwartz S, et al. (2001) Maternal folate polymorphisms and the etiology of human nondisjunction. Am J Hum Genet 69: 434-439.
  113. Grillo LB, Acácio GL, Barini R, Pinto W Jr, Bertuzzo CS (2002) Mutations in the methylene-tetrahydrofolate reductase gene and Down syndrome. Cad Saude Publica 18: 1795-1797.
  114. Biselli JM, de Souza GC, Sierra DB, Marques J, Goloni-Bertollo EM, et al. (2006) Investigação dos polimorfismos maternos C677T e A1298C dogene MTHFR e A66G do gene MTRR como fatores de riscopara a síndrome de Down. Arq Ciênc Saúde 13: 198-201.
  115. Oliveira KC, Bianco B, Verreschi IT, Guedes AD, Galera BB, et al. (2008) Prevalence of the polymorphism MTHFR A1298C and not MTHFR C677T is related to chromosomal aneuploidy in Brazilian Turner Syndrome patients. Arq Bras Endocrinol Metabol 52: 1374-1381.
  116. Patterson D (2008) Folate metabolism and the risk of Down syndrome. Downs Syndr Res Pract 12: 93-97.
  117. Wang SS, Qiao FY, Feng L, Lv JJ (2008) Polymorphisms in genes involved in folate metabolism as maternal risk factors for Down syndrome in China. J Zhejiang Univ Sci B 9: 93-99.
  118. Castro R, Rivera I, Ravasco P, Camilo ME, Jakobs C, et al. (2004) 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298A-->C mutations are associated with DNA hypomethylation. J Med Genet 41: 454-458.
  119. Guenther BD, Sheppard CA, Tran P, Rozen R, Matthews RG, et al. (1999) The structure and properties of methylenetetrahydrofolate reductase from Escherichia coli suggest how folate ameliorates human hyperhomocysteinemia. Nat Struct Biol 6: 359-365.
  120. Kang SS, Zhou J, Wong PW, Kowalisyn J, Strokosch G (1988) Intermediate homocysteinemia: a thermolabile variant of methylenetetrahydrofolate reductase. Am J Hum Genet 43: 414-421.
  121. Nishio K, Goto Y, Kondo T, Ito S, Ishida Y, et al. (2008) Serum folate and methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism adjusted for folate intake. J Epidemiol 18: 125-131.
  122. Bailey LB, Gregory JF 3rd (1999) Polymorphisms of methylenetetrahydrofolate reductase and other enzymes: metabolic significance, risks and impact on folate requirement. J Nutr 129: 919-922.
  123. Weisberg I, Tran P, Christensen B, Sibani S, Rozen R (1998) A second genetic polymorphism in methylenetetrahydrofolate reductase (MTHFR) associated with decreased enzyme activity. Mol Genet Metab 64: 169-172.
  124. Suarez-Kurtz G (2004) Pharmacogenomics in admixed populations: the Brazilian pharmacogenetics/pharmacogenomics network--REFARGEN. Pharmacogenomics J 4: 347-348.
  125. Mannervik B, Alin P, Guthenberg C, Jensson H, Tahir MK, et al. (1985) Identification of three classes of cytosolic glutathione transferase common to several mammalian species: correlation between structural data and enzymatic properties. Proc Natl Acad Sci U S A 82: 7202-7206.
  126. Hayes JD, Pulford DJ (1995) The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance. Crit Rev Biochem Mol Biol 30: 445-600.
  127. de Oliveira Hiragi C, Miranda-Vilela AL, Rocha DM, de Oliveira SF, Hatagima A, et al. (2011) Superoxide dismutase, catalase, glutathione peroxidase and gluthatione S-transferases M1 and T1 gene polymorphisms in three Brazilian population groups. Genet Mol Biol 34: 11-18.
  128. Sherratt PJ, Hayes JD (2002) Glutathione S-transferases. In: Ioannides C (Ed.). Enzyme Systems that Metabolise Drugs and Other Xenobiotics, Chapter 9. John Wiley & Sons Ltda, New Jersey, USA. 319-352.
  129. Cotton SC, Sharp L, Little J, Brockton N (2000) Glutathione S-transferase polymorphisms and colorectal cancer: a HuGE review. Am J Epidemiol 151: 7-32.
  130. Landi S (2000) Mammalian class theta GST and differential susceptibility to carcinogens: a review. Mutat Res 463: 247-283.
  131. García-Closas M, Kelsey KT, Hankinson SE, Spiegelman D, Springer K, et al. (1999) Glutathione S-transferase mu and theta polymorphisms and breast cancer susceptibility. J Natl Cancer Inst 91: 1960-1964.
  132. Hayes JD, Strange RC (2000) Glutathione S-transferase polymorphisms and their biological consequences. Pharmacology 61: 154-166.
  133. Pemble S, Schroeder KR, Spencer SR, Meyer DJ, Hallier E, et al. (1994) Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism. Biochem J 300: 271-276.
  134. Pearson WR, Vorachek WR, Xu SJ, Berger R, Hart I, et al. (1993) Identification of class-mu glutathione transferase genes GSTM1-GSTM5 on human chromosome 1p13. Am J Hum Genet 53: 220-233.
  135. Fryer AA, Zhao L, Alldersea J, Pearson WR, Strange RC (1993) Use of site-directed mutagenesis of allele-specific PCR primers to identify the GSTM1 A, GSTM1 B, GSTM1 A,B and GSTM1 null polymorphisms at the glutathione S-transferase, GSTM1 locus. Biochem J 295: 313-315.
  136. Biernaux C, Loos M, Sels A, Huez G, Stryckmans P (1995) Detection of major bcr-abl gene expression at a very low level in blood cells of some healthy individuals. Blood 86: 3118-3122.
  137. Bose S, Deininger M, Gora-Tybor J, Goldman JM, Melo JV (1998) The presence of typical and atypical BCR-ABL fusion genes in leukocytes of normal individuals: biologic significance and implications for the assessment of minimal residual disease. Blood 92: 3362-3367.
  138. Anastasi J, Moinuddin R, Daugherty C (1999) The juxtaposition of ABL with BCR and risk for fusion may come at the time of BCR replication in late S-phase. Blood 94: 1137-1138.
  139. Su YC, Chen YC, Li SC, Lee CC, Tung YT (2009) Detection of Hpdel in healthy individuals and cancer patients in Taiwan. Clin Chem Lab Med 47: 745-749.
  140. Sadrzadeh SM, Bozorgmehr J (2004) Haptoglobin phenotypes in health and disorders. Am J Clin Pathol 121: S97-104.
  141. Wobeto VPA, Zaccariotto TR, Sonati MF (2008) Polymorphism of human haptoglobin and its clinical importance. Genet Mol Biol 31: 602-620.
  142. Huntoon KM, Wang Y, Eppolito CA, Barbour KW, Berger FG, et al. (2008) The acute phase protein haptoglobin regulates host immunity. J Leukoc Biol 84: 170-181.
  143. Guéye PM, Glasser N, Férard G, Lessinger JM (2006) Influence of human haptoglobin polymorphism on oxidative stress induced by free hemoglobin on red blood cells. Clin Chem Lab Med 44: 542-547.
  144. Moreira LR, Miranda-Vilela AL, Silva IC, Akimoto AK, Klautau-Guimarães MN, et al. (2009) Antioxidant effect of haptoglobin phenotypes against DNA damage induced by hydrogen peroxide in human leukocytes. Genet Mol Res 8: 284-290.
  145. Carter K, Worwood M (2007) Haptoglobin: a review of the major allele frequencies worldwide and their association with diseases. Int J Lab Hematol 29: 92-110.
  146. Miranda-Vilela AL, Akimoto AK, Alves PC, Hiragi CO, Penalva GC, et al. (2009) Haptoglobin gene subtypes in three Brazilian population groups of different ethnicities. Genet Mol Biol 32: 456-461.
  147. Langlois MR, Delanghe JR (1996) Biological and clinical significance of haptoglobin polymorphism in humans. Clin Chem 42: 1589-1600.
  148. Smithies o (1955) Zone electrophoresis in starch gels: group variations in the serum proteins of normal human adults. Biochem J 61: 629-641.
  149. Smithies O, Connell GE, Dixon GH (1962) Inheritance of haptoglobin subtypes. Am J Hum Genet 14: 14-21.
  150. Jobim M, Jobim LF (2008) Natural killer cells and immune surveillance. J Pediatr (Rio J) 84: S58-67.
  151. Melamed-Frank M, Lache O, Enav BI, Szafranek T, Levy NS, et al. (2001) Structure-function analysis of the antioxidant properties of haptoglobin. Blood 98: 3693-3698.
  152. Kaneta Y, Kagami Y, Tsunoda T, Ohno R, Nakamura Y, et al. (2003) Genome-wide analysis of gene-expression profiles in chronic myeloid leukemia cells using a cDNA microarray. Int J Oncol 23: 681-691.
  153. Akimoto AK, Miranda-Vilela AL, Alves PC, Pereira LC, Lordelo GS, et al. (2010) Evaluation of gene polymorphisms in exercise-induced oxidative stress and damage. Free Radic Res 44: 322-331.
  154. Miranda-Vilela AL, Alves PCZ, Akimoto AK, Lordelo GS, Klautau-Guimarães MN, et al. (2011) Under increased hydrogen peroxide conditions, the antioxidant effects of pequi oil (Caryocar brasiliense Camb.) to decrease DNA damage in runners are influenced by sex, age and oxidative stress-related genetic polymorphisms. Free Rad Antiox 1: 27-39.
Citation: Miranda-Vilela AL, Lordelo GS (2013) Role of Methylenetetrahydrofolate Reductase (Mthfr), Glutathione S-transferases (Gsts M1 and T1) and Haptoglobin (Hp) Gene Polymorphisms in Susceptibility to Chronic Myeloid Leukemia (Cml). J Hematol Thromb Dis 1:103.

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