GAD1 and type 2 diabetes mellitus: An OGTT was performed in these affected adults (Fig. 1c): this verified impaired glucose tolerance in family member II-2, who had developed a BMI of 38.9 kg/m2 and type 2 diabetes with no autoantibodies detectable against GAD or against tyrosine phosphatase-related islet antigen 2 (IA-2) up to the time of this examination at age 35 years.