The p.R89H (proinsulin Tokyo), p.R89P (proinsulin Oxford), and p.R89L (proinsulin Kyoto) are processing site mutations at the C-peptide to A-chain junction, which cause issues with C-peptide cleaving, leading to hyperproinsulinemia and resulting in NDM [11,41,52,53,54]. The gene discussed is INS; the disease is hyperproinsulinemia.