Postpartum OGTT revealed diabetes mellitus (2 h plasma glucose >200 mg/dL) with low blood insulin values (5–23.6 mU/mL), C-peptide 1.1 ng/mL, and anti-GAD Ab positivity (>2000 U/L), while HbA1c was 5.9%. This evidence concerns the gene GAD1 and diabetes mellitus.