The maintenance of chromosome stability during cell division is crucial for inheritance of complete genetic information by progeny cells. Errors in mechanisms safeguarding genomic stability during cell division can result in chromosome aberrations during gametogenesis and development that may manifest as disease phenotypes. Structural maintenance of chromosomes (SMC) protein complexes play important roles in chromosome organization and function and impact a wide variety of chromosomal transactions. The conserved Smc5/6 complex is essential for viability, repair of DNA double strand breaks and recovery of collapsed replication forks and is crucial for chromosome stability. This mini review is focussed on hMMS21/NSMCE2, the human homolog of MMS21/NSE2 that is a non-smc subunit of the Smc5/6 complex having SUMO E3 ligase activity, and aims to provide insights into the role of hMMS21/NSMCE2 in human development and disease associated with deficiency of NSMCE2.