Glutamic acid decarboxylase 65 (GAD65; Gad2), one of the two mammalian enzymes that synthesize GABA from glutamate (the other being GAD67, Gad1), is expressed in human beta cells, and is a major autoantigen in type 1 diabetes (T1D) (2). This evidence concerns the gene GAD1 and type 1 diabetes mellitus.