Abstract: The cytotoxic T Lymphocyte-Associated Antigen 4 gene (CTLA4) encodes the T cell receptor involved in the control of T cell proliferation and mediates T cell apoptosis. The receptor protein is a specific T lymphocyte surface antigen that is detected on cells only after antigen presentation. Thus, CTLA4 is directly involved in both immune and autoimmune responses and may be involved in the pathogenesis of multiple T cell-mediated autoimmune disorders. In this research the work was to investigate whether this gene conferred susceptibility to IDDM in a Russian population. The researchers carried out family studies using two polymorphic markers at the CTLA4 gene locus: codon 17 dimorphism and the dinucleotide microsatellite in the 3' untranslated region. The Ala17 allele of the CTLA4 gene was preferentially transmitted from parents to diabetic offspring (p<0.0001) as shown by the combined Transmission/Disequlibrium Test (TDT) and Sib TDT (S-TDT) analysis.