GAD1 and diabetes mellitus: The prevalence rate of GAD seropositivity was 44% in T1D patients, GAD was positive in 2 patients with T2D and none of the other groups. GAD-positive and GAD-negative participants had similar characteristics (age of onset and duration of diabetes).***The GAD threshold of 1 U/ml may not reflect the optimal cut off for the population and has unclear specificity, although the small control population provides some reassurance.