Genetics of type I diabetes

Type I diabetes mellitus is a T-cell-mediated autoimmune disease characteri zed by the selective destruction of pancreatic beta cells. Susceptibility t o the disease is determined by a combination of genetic and environmental f actors. The genetic factors are termed 'susceptibility genes' as they modif y the risk of diabetes but are neither necessary nor sufficient for disease to develop. A large number of chromosomal regions have been identified as containing potential diabetes susceptibility genes. The IDDM1 locus, which encompasses the major histocompatibility complex on chromosome 6, is the ma jor genetic risk factor. The HLA-DQ genes are the primary susceptibility ge nes within this region, although other genes may also contribute. The IDDM2 locus maps to a variable number of tandem repeats in the insulin gene regi on on chromosome II. Further research is necessary to determine the precise location and identity of other diabetes susceptibility genes.