GAD1 and type 1 diabetes mellitus: Although genetic markers (particularly HLA Class II susceptibility alleles) and serum aAbs against the β-cell Ags insulin, glutamic acid decarboxylase (GAD), insulinoma-associated protein 2 (IA-2), and zinc transporter 8 (ZnT8) greatly help to stratify T1D risk, they fall short in accuracy, as they can predict the risk but not the time course of disease development (i.e., the “if”, but not the “when”), and much less when only one aAb marker is present.