NSMCE2 is an E3 SUMO-protein ligase component of the SMC5-SMC6 complex that mediates protein sumoylation to regulate DNA repair and chr8 stability. The complex functions in DNA double-strand break repair by homologous recombination 12 and promotes sister chr8 cohesion by recruiting cohesin complexes to breaks 1. NSMCE2 catalyzes sumoylation of shelterin complex components and other substrates including SMC6L1, RAD51AP1, and cohesin subunits 34, with ligase activity required for preventing DNA damage-induced apoptosis and facilitating telomere maintenance via recombination in ALT cells 3. Clinically, NSMCE2 hypomorphic mutations cause Seckel syndrome 10 (primordial dwarfism with insulin resistance) 5, with patient cells showing increased chr8 aberrations and impaired recovery from replication stress 5. NSMCE2 deletion phenocopies Bloom syndrome characteristics including micronuclei accumulation and elevated recombination 6. In cancer, NSMCE2 is upregulated via super-enhancers in breast cancer, correlating with poor prognosis and chemotherapy resistance 7, while elevated expression in hepatocellular carcinoma promotes tumor development through SUMOylation-dependent mechanisms 8. Unexpectedly, NSMCE2's tumor-suppressive function in mice operates independently of SUMO ligase activity 6.