To date, ten genes have been linked to isolated CHI, explaining 45–55% of the cases (ABCC8, KCNJ11, GLUD1, GCK, HADH, HNF1A, HNF4A, SLC16A1, UCP2, HK1) and more than 28 genes or chromosomal abnormalities have been reported for syndromic CHI. The gene discussed is HNF4A; the disease is congenital isolated hyperinsulinism.