Type 1 diabetes (T1D) is a complex, multigenic disease. The first reports of genetic association to T1D were for the human leukocyte antigen (HLA) region (Singal and Blajchman 1973; Cudworth and Woodrow 1974; Nerup et al.1974).ype 1 diabetes (T1D) is a complex, multigenic disease. The first reports of genetic association to T1D were for the human leukocyte antigen (HLA) region (Singal and Blajchman 1973; Cudworth and Woodrow 1974; Nerup et al.