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Cystinuria Revisited: Presentations with Calcium-Containing Stones Demands Vigilance and Screening in the Stone Clinic
Medical & Surgical Urology

Medical & Surgical Urology
Open Access

ISSN: 2168-9857

Commentary - (2014) Volume 3, Issue 3

Cystinuria Revisited: Presentations with Calcium-Containing Stones Demands Vigilance and Screening in the Stone Clinic

Sarah J Rice1,2, David T Thwaites2, Jan Halbritter3 and John A Sayer1,4*
1Institute of Genetic Medicine, International Centre for Life, Newcastle University, Central Parkway, Newcastle upon Tyne, NE1 3BZ, UK
2Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
3Division of Endocrinology and Nephrology, Department of Internal Medicine, University Clinic Leipzig, Germany
4Renal Unit, Newcastle upon Tyne Hospitals NHS Foundation Trust, Freeman Road, Newcastle upon Tyne, NE7 7DN, UK
*Corresponding Author: John A Sayer, Institute of Genetic Medicine, New Castle University, Newcastle, UK, Tel: +44 191 2418608 Email:

Abstract

Abstract : Cystinuria is an inherited disorder resulting in urinary wasting of dibasic amino acids and often the formation of cystine stones. Cystinuria is often complicated by frequently recurring cystine stones which can form staghorn calculi. The clinical features of cystinuria can be extremely variable leading to missed or delayed diagnosis. Indeed, cystinuria may present with “idiopathic” nephrolithiasis and even calcium containing stones and patients presenting with calculi should be screened for this disorder to allow for appropriate medical and surgical management.

Introduction

Cystinuria is an inherited renal disorder resulting in urinary wasting of dibasic amino acids and often the formation of cystine stones. Cystinuria is often complicated by frequently recurring stones, large stones and staghorn calculi, which may result in nephrectomy and renal failure [1]. Cystinuria is caused by mutations in two genes, SLC3A1 and SLC7A9. Cystinuria is often quoted as an autosomal recessive disease, but infact it may be inherited in multiple ways: an autosomal recessive manner, an autosomal dominant manner (often with incomplete penetrance), or in a digenic manner (where mutations are present in both genes). Within SLC3A1 and SLC7A9, point mutations, multi-exon deletions and duplications and genomic rearrangements have all been described, leading to a loss of function of their encoded proteins. SLC3A1 encodes the accessory protein rBAT [2] whilst SLC7A9 encodes the catalytic transport protein b0,+AT [3]. Together these proteins form a heterodimer that functions as an amino acid transport system known as system b0,+, an electrogenic exchanger of extracellular dibasic amino acids and cystine for intracellular zwitterionic amino acids [4,5]. Within the kidney, system b0,+ is expressed at the luminal membrane in the renal proximal tubule and mediates reabsorption of cystine, ornithine, lysine and arginine [5].

The clinical features of cystinuria can be extremely variable leading to missed or delayed diagnosis. Clinical variability is mostly seen in patients with heterozygous mutations and a recent study highlights this fact [6]. Here, a genetic screen of 272 renal stone formers and patients with nephrocalcinosis identified 52 likely causative mutations in genes known to lead to monogenic renal stone formation. Surprisingly, within this cohort there were 6 patients in whom known pathogenic heterozygous mutations in SLC7A9 were detected, where there was no prior clinical suspicion of cystinuria [6]. Three of these patients presented with calcium containing stones (two with SLC7A9 mutation p.Gly105Arg [7], and the other p.Asn206Glufs*3 [8]) whilst the others were labelled as having idiopathic nephrocalcinosis/nephrolithiasis or hypercalciuria (two with SLC7A9 mutation p.Ala182Thr [3] and another with p.Gly105Arg [7]).

This observation is a timely reminder that patients with cystinuria may present with “idiopathic” nephrolithiasis and even calcium containing stones. Cystinuria may also be associated with serum biochemical abnormalities including hyperuricaemia [9].

Other descriptions of cystinuria patients forming calcium stones may be found in the literature. Early presentations with calcium containing stones are possible [10]. In contrast, Cupisiti et al. describe a recurrent calcium stone former in whom the diagnosis of cystinuria was delayed until the patient was 72 years of age [11]. Elkoushy and Andonian also describe patients with medium to low levels of cystinuria (presumed to be heterozygous carriers of mutations) with both calcium oxalate and uric acid stone formation [12]. This observation was also corroborated by in vitro data, prompting consideration of cystinuria as a risk factor for calcium stone disease [13]. Consequently, this led to an urge to broadly screen for cystinuria, especially in those patients with unexplained stones [14]. A recent review from St Thomas’ Hospital confirmed the fact that even in known cystinuria patients, typical radiolucent cystine stones are not the rule. Here, 16 out of 70 cystinuria patients in this cohort had radio opaque stones [15].

It can be postulated that even with low urinary cystine excretion rates, as seen in patients with heterozygous mutations, cystine crystals form a nidus, which then allows the nucleation of calcium and uric acid crystals. Even once the diagnosis of cystinuria is established and treatment has begun with agents to alkalinise the urine, there may also be a risk of calcium phosphate crystal precipitation [16].

In light of these recent findings by Halbritter et al. [6] and a body of historical reports, we again emphasize the need for biochemical screening of urine for cystinuria for all idiopathic stone formers, where undetected cystinuria patients may be identified [17]. Screening for cystinuria is straightforward and may be performed on a spot urine sample [15,18].

Given that there are 2 underlying genes which lead to cystinuria, whose inheritance patterns and biochemical phenotypes are variable, the detection or clinical suspicion of cystinuria should prompt molecular genetic studies. With the advent of next generation sequencing techniques, these studies will become more accessible and will lead to important correlations between genetic variants and disease presentations and long term outcomes. Renal stone patients deserve a precise diagnosis of their cause of calculi as preventive measures can then be tailored towards the underlying cause.

Acknowledgements

This work was generously supported by the Northern Counties Kidney Research Fund. SJR was supported by an MRC PhD studentship.

References

  1. Sumorok N, Goldfarb DS (2013) Update on cystinuria. See comment in PubMed Commons below CurrOpinNephrolHypertens 22: 427-431.
  2. Bertran J, Werner A, Chillarón J, Nunes V, Biber J, et al. (1993) Expression cloning of a human renal cDNA that induces high affinity transport of L-cystine shared with dibasic amino acids in Xenopus oocytes. J BiolChem 268: 14842-14849.
  3. Feliubadaló L, Font M, Purroy J, Rousaud F, Estivill X, et al. (1999) Non-type I cystinuria caused by mutations in SLC7A9, encoding a subunit (bo,+AT) of rBAT. Nat Genet 23: 52-57.
  4. Chillarón J, Estévez R, Mora C, Wagner CA, Suessbrich H, et al. (1996) Obligatory amino acid exchange via systems bo,+-like and y+L-like. A tertiary active transport mechanism for renal reabsorption of cystine and dibasic amino acids. J BiolChem 271: 17761-17770.
  5. Fotiadis D, Kanai Y, Palacín M (2013) The SLC3 and SLC7 families of amino acid transporters. Mol Aspects Med 34: 139-158.
  6. Halbritter J, Baum M, Hynes AM, Rice SJ, Thwaites DT et al. (2014) Fourteen monogenic genes account for 15% of nephrolithiasis / nephrocalcinosis. J Am SocNephrol In Press
  7. Bisceglia L, Fischetti L, Bonis PD, Palumbo O, Augello B, et al. (2010) Large rearrangements detected by MLPA, point mutations, and survey of the frequency of mutations within the SLC3A1 and SLC7A9 genes in a cohort of 172 cystinuric Italian patients. Mol Genet Metab 99: 42-52.
  8. Leclerc D, Boutros M, Suh D, Wu Q, Palacin M, et al. (2002) SLC7A9 mutations in all three cystinuria subtypes. Kidney Int 62: 1550-1559.
  9. Meloni FR, Canary JJ (1967) Cystinuria with hyperuricemia. JAMA 200: 257-259.
  10. O'Regan S, Robitaille P, Mongeau JG, Homsy Y (1980) Cystine calcium bladder calculus in a 2-year-old child. J Urol 123: 770.
  11. Cupisti A, Farnesi I, Armillotta N, Francesca F (2012) Staghorncystine stone in a 72-year-old recurrent calcium stone former. ClinNephrol 78: 76-80.
  12. Elkoushy MA, Andonian S (2012) Characterization of patients with heterozygous cystinuria. Urology 80: 795-799.
  13. Martins MC, Meyers AA, Whalley NA, Rodgers AL (2002) Cystine: a promoter of the growth and aggregation of calcium oxalate crystals in normal undiluted human urine. J Urol 167: 317-321.
  14. Thomas K, Wong K, Withington J, Bultitude M, Doherty A (2014) Cystinuria-a urologist's perspective. Nat Rev Urol 11: 270-277.
  15. Evan AP, Coe FL, Lingeman JE, Shao Y, Matlaga BR, et al. (2006) Renal crystal deposits and histopathology in patients with cystine stones. Kidney Int 69: 2227-2235.
  16. Carpentier PJ, Kurth KH, Blom W, Huijmans JG (1983) Heterozygouscystinuria and calcium oxalate urolithiasis. J Urol 130: 302-304.
  17. Sayer JA, Moochhala SH, Thomas DJ (2010) The medical management of urolithiasis. Br J Med SurgUrol
Citation: Rice SJ, Thwaites DT, Halbritter J, Sayer JA (2014) Cystinuria Revisited: Presentations with Calcium-Containing Stones Demands Vigilance and Screening in the Stone Clinic. Med Surg Urol 3:140.

Copyright: © 2014 Rice SJ, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.