CTLA4 and type 1 diabetes mellitus: In citing examples of candidate common susceptibility genes involved in immune regulation, cytotoxic T lymphocyte-associated antigen 4 (CTLA4) suppresses T cell activation [16], forkhead box P3 (FOXP3) is involved in the differentiation of T regulatory cells (T-regs), the IL-2 receptor alpha/CD25 gene also affects the development and the function of T-regs, and the TNF-α gene, located on chromosome 6p21.3, is at the basis of the increased risk for the association of T1D and autoimmune thyroid disease (rev.