The 64 kDa protein originally described by Baekkeskov et al. was subsequently shown to represent two major targets of autoimmunity in type 1 diabetes: the 65 kDa isoform of glutamic acid decarboxylase (GAD65) and a tyrosine phosphatase-like protein, IA-2 [10, 11]. Here, PTPRN is linked to type 1 diabetes mellitus.