CHI-F is a somatic-recessive endocrine disorder arising through a combination of events involving deregulation of imprinting in region Ch.11p15.5 and a somatic reduction to homozygosity of a paternal gene defect in either ABCC8 or KCNJ11. At least 12 imprinted genes are known to be encoded by the Ch.11p15.5 imprinting domain and several are thought to be involved with β-cell overgrowth—H19, P57KIP2, and IGF2, in CHI-F (11, 15). The gene discussed is KCNJ11; the disease is congenital isolated hyperinsulinism.