Type 1 diabetes mellitus due to pancreatic islets anomalies was reported in less than 1% of the subjects after a few months to a few years of drug exposure, mostly due to anti-PD-1 (programmed cell death protein) and anti-PD-L1 (programmed cell death protein ligand) antibodies rather than anti-CTLA-4 (cytotoxic T-lymphocyte associated protein). The gene discussed is PDCD1; the disease is diabetes mellitus.