Autoimmune polyendocrine syndromes (APS) are a heterogeneous group of diseases characterized by the presence of autoimmune dysfunction of 2 or more endocrine glands and other non-endocrine organs. The components of the syndrome can manifest throughout life: in childhood-APS type 1 (the juvenile type) and in adulthood-APS type 2, 3, and 4 (the adult types). Adult types of APS are more common in clinical practice. It is a polygenic disease associated with abnormalities in genes encoding key regulatory proteins of the major histocompatibility complex (MHC). The search of for candidate genes responsible for mutations in adult APS is continuing. Genetic predisposition is insufficient for the manifestation of the APS of adults, since the penetrance of the disease, even among monozygotic twins, does not approach 100% (30-70%). The article presents the case of isolated Addison's disease and APS type 2 in monozygotic twins with a revealed compound heterozygosity in the candidate gene VTCN1.