Biallelic mutations in NEUROG3 result in severe congenital malabsorptive diarrhea due to a lack of enteroendocrine cells in the gut (1) and diabetes with a variable age of onset, in keeping with the role of neurogenin 3 in pancreatic endocrine differentiation during embryonic development (1, –, 3). The gene discussed is NEUROG3; the disease is diabetes mellitus.