PTPRN and type 1 diabetes mellitus: Ironically, positivity to glutamic acid decarboxylase (GAD65), tyrosine phosphatase-like protein (IA-2), proinsulin/insulin (IAA), and zinc transporter 8 (ZnT8) (autoantibodies) can signal a risk for T1D, yet many testing positive neither develop insulitis nor T1D [73,74,75].