Non-syndromal CHI has been associated with mutations in a least nine different key genes, namely ABCC8, KCNJ11, GCK, GLUD1, HADH, HK1, HNF1A, HNF4A, and SLC16A1 (2), of which inactivating mutations in the KATP-channel genes ABCC8 and KCNJ11 are the most common, accounting for about 90% of the diazoxide-unresponsive CHI patients (3, 4). The gene discussed is HNF1A; the disease is congenital isolated hyperinsulinism.