Haploinsufficiency of PTEN results in a lethal T cell-mediated autoimmune disorder characterized by spontaneous T cell activation and reduced Fas-mediated activation-induced cell death.74 Conditional deletion of PTEN using the T cell-specific CD4-Cre in mice leads to an autoimmune phenotype characterized by spontaneous activation and differentiation of effector T cells.75,76 PTEN activity also regulates Treg function. The gene discussed is PTEN; the disease is autoimmune disease.