RAD21 belongs to the cohesin complex family of genes that encode protein subunits of the cohesion complex, which regulates chromosomal segregation. is a member of the cohesin complex that regulates chromosome segregation during meiosis and mitosis. Loss of function mutations of RAD21 have been described throughout the gene in approximately 1% of cases of myelodysplasia, 1-5% of acute myeloid leukemia (AML), 1% of chronic myeloid leukemia and tend to be mutually exclusive of other mutations in the other components of the cohesin complex (ie, STAG1, SMC3, STAG2, SMC1A). In AML, mutations in the cohesin complex genes tend to be associated with mutations in NPM1. Cohesin complex mutations do not have clear prognostic impact in AML. Cohesin complex mutations are associated with an unfavorable prognosis in myelodysplastic syndrome, and are more frequently found in patients with high IPSS scores and secondary acute myeloid leukemia.