STAG2 encodes a subunit of the cohesin complex, the protein machinery that holds sister chromatids together and ensures their accurate separation during cell division. Disruption of this gene is linked to cohesinopathies, developmental conditions marked by intellectual disability, distinctive facial features, and speech disorders. STAG2 acts as a tumor suppressor in cancer, where inactivating changes cause aneuploidy and chromosomal instability and are found across many tumor types, including melanoma, bladder carcinoma, Ewing sarcoma, glioblastoma, and myeloid cancers such as myelodysplastic syndrome and acute myeloid leukemia. In myeloid malignancies, STAG2 alterations are associated with worse overall survival but better responses to certain treatments.

This nonsense change (p.Glu811Ter) would truncate the cohesin subunit STAG2, a mechanism consistent with the gene's established tumor-suppressor role, where inactivating mutations drive aneuploidy and chromosomal instability. However, germline significance remains uncertain: population-absence evidence alone (PM2) does not establish pathogenicity, and no disease-specific observations exist for this exact variant.