GAD2 and type 1 diabetes mellitus: The most common and abundant autoantigens in T1D patients and high-risk individuals are (pro)-insulin (P)INS, glutamic-acid decarboxylase of 65 kDa (GAD65), tyrosine phosphatase-like protein ICA152 (IA-2), and zinc transporter 8 (ZnT8) (114, 115).