GAD1 and type 1 diabetes mellitus: The seroprevalence of IA-2 was 19% in black and 41% in white participants while GAD was 60% in blacks and 66% in the white participants. The seroprevalence of GAD and IA-2 was significantly lower in black participants with age of onset ≥ 21 years.***Data suggests that GAD autoantibody may be long-standing autoimmune marker in this population of T1D given that the median diabetes duration > 5 years.