PTPRN and type 1 diabetes mellitus: In T1DM patients, specific HLA alleles correlate with an increased risk of developing diabetes, and autoimmune recurrence after pancreas transplantation poses a significant challenge, as type 1 diabetes can reappear in the graft even without detectable glutamic acid decarboxylase (GAD) and insulinoma-associated protein 2 (IA-2) autoantibodies [56,57,58].