Recently, in a Japanese cohort of autoimmune diabetic patients (type 1A), CD4+ T cells expressed lower levels of PD-1 than those of patients with type 1 (fulminant type 1) or type 2 diabetes or healthy control subjects, which may indicate that CD4+ T cells with decreased PD-1 expression result in Type 1A autoimmune diabetes via T-cell activation (103). Here, PDCD1 is linked to type 2 diabetes mellitus.