DDC and diabetes mellitus: T1D occurs in only 1–18% of APS-1 patients but high titer autoantibodies against diabetes-related autoantigens, such as glutamic acid decarboxylase isoform 65 (GAD65), glutamic acid decarboxylase isoform 67 (GAD67), aromatic l-amino acid decarboxylase (AADC), and islet antigen 2 (IA-2) have been detected in 30–66% of APS-1 patients (26, 27).