GAD2 and type 1 diabetes mellitus: Several studies on blood samples from monozygotic twins discordant for T1D have demonstrated the relevance of altered DNA methylation in immune cells to T1D pathogenesis, with significant methylation changes at genes of immediate relevance to T1D pathogenesis such as HLA genes, INS, IL-2RB, CD226, NFKB1A, TNF, INS-IGF2, CLEC16A, and GAD2 (163, 168, 169).