We performed insulin and glucagon secretion studies by perifusion of islets isolated from 19 normoglycemic organ donors with no AAbs against islet antigens (control), 9 normoglycemic organ donors positive for AAbs against GAD (GADA+), and 6 organ donors with T1D (Supplemental Table 1; supplemental material available online with this article; https://doi.org/10.1172/JCI156243DS1). This evidence concerns the gene GCG and type 1 diabetes mellitus.