Familial risk, pathogenesis, Clinical onset, and treatment of diabetes mellitus vary according to etiology. Although Type 2 diabetes has a higher familial risk, more is known about the genetics of type 1 diabetes. Genes contributing 60[Per cnt] to 65[per cnt] of sesceptibility to type 1 diabetes is associated with susceptibility genes in the HLA region on chromosome 6p21 and the insulin gene on chromosome 11p15, and at lease eight additional susceptibility genes are under investigation, Islet cytoplasmic antibodies provide humoral evidence of type 1 diabetes risk. Only 10[per cnt] of the genes contributing susceptibility to type 2 diabetes mellitus are known, and they are primarily associated with uncommon subtypes of the disorder. The insulin receptor gene on chromosome 19p13 and at lease five glucose transporter genes contribute to type 2 diabetes susceptibility, and further associations may emetge from study of the glycogen synthase gene, the glucokinase gene, the MODY genes, and the leptin gene. Diabetes comorbidities may result from genetic and environmental susceptibilities independently or in combination.