To date, several loci conferring susceptibility to T1D have been identified, i.e. the human leucocyte antigen complex in chromosome 6p21.3, the insulin gene in 11p15.5 and the cytotoxic T lymphocyte-associated antigen-4 (CTLA4) gene in 2q33.2 [2]. The gene discussed is CTLA4; the disease is type 1 diabetes mellitus.