KCNJ11 and congenital isolated hyperinsulinism: In focal CHI, mutations in the ABCC8 and KCNJ11 genes in combination with a specific loss of maternal alleles in the imprinted chromosome region 11p15, lead to abnormal proliferation and morphogenesis of β-cells, resulting in the formation of the hyperplastic focus of hyperfunctioning β-cells [1,14].