PTPRN and type 1 diabetes mellitus: Interestingly, IA-2 and GAD have been defined as a key autoantigen in T1D on the basis of the predictive value of anti-IA2 and anti-GAD autoantibodies in prediabetic individuals, while IGRP and IAPP have not been defined as key targets of autoantibodies in T1D in the human.