In focal CHI, a paternal monoallelic recessive mutation in ABCC8 or KCNJ11, followed by a somatic loss of heterozygosity of the 11p15 maternal allele in a restricted pancreatic region, results in the formation of focal adenomatous hyperplasia with structurally absent or non-functional KATP channels within the focus [1,14]. This evidence concerns the gene KCNJ11 and congenital isolated hyperinsulinism.