Genetics of Type 1 diabetes mellitus

Type 1 diabetes or insulin-dependent diabetes mellitus (IDDM) is the archetypal example of a T cell-mediated autoimmune disease characterised by selective destruction of a single cell type: the insulin-producing beta-cells of the pancreatic islets of Langerhans. The pathogenic equation for IDDM presents a complex interrelation of genetic and environmental factors, most of which have yet to be identified. Based on the observed familial aggregation of IDDM, it is certain that there is a decided heritable genetic susceptibility for developing autoimmune diabetes. The well-known association of IDDM with certain human histocompatibility leukocyte antigen (HLA) alleles of the major histocompatibility complex (MHC) was a major step toward understanding the role of inheritance in IDDM. Landmark molecular biological investigations of diabetes HLA susceptibility genes provided great potential for insights into the molecular basis for the autoimmune nature of the disease, beginning a story that continues to unfold. Although the association of certain HLA alleles with IDDM is very strong, this genetic locus is estimated to account for less than 50% of genetic contributions to disease susceptibility. The search for non-HLA susceptibility genes has received great attention in recent years. Albeit genome wide searches are wrought with controversy, such studies have suggested the association of numerous non-MHC loci with Type 1 diabetes that will require careful follow-up investigation. Cell biological and genetic functional analyses will provide clues that are indispensable for further progress. The necessary studies include research on immunological abnormalities that are present many years before the clinical onset of Type 1 diabetes.