Activating KCNJ11 mutations are the most common cause of permanent neonatal diabetes mellitus (PNDM), diagnosed in the first 6 months of life.1KCNJ11 encodes Kir6.2, the pore-forming subunit of the ATP-sensitive potassium (KATP) channel that, in the beta cell, closes in response to metabolically generated ATP, causing beta cell depolarization and insulin secretion. The gene discussed is KCNJ11; the disease is neonatal diabetes mellitus.