GAD1 and diabetes mellitus: Exclusion criteria included history of type 1 or secondary diabetes, antiglutamic acid decarboxylase (GAD) antibody positivity, absence of β-cell function (fasting C-peptide concentration <1 ng/mL or glucagon-stimulated C-peptide concentration <1.5 ng/mL), and presence of severe complications of diabetes (proliferative retinopathy, serum creatinine >2 mg/dL, vascular complications, or severe neuropathy).