Congenital hyperinsulinism and glucose hypersensitivity in homozygous and heterozygous carriers of Kir6.2 (KCNJ11) mutation V290M mutation. KATP channel inactivation mechanism and clinical management.

Objective: The ATP-sensitive K+-channel (KATP) controls insulin secretion from the islet. Gain- or loss-of-function mutations in channel subunits underlie human neonatal diabetes mellitus (NDM) and congenital hyperinsulinism (HI), respectively. In this study we sought to identify the mechanistic basis of KATP-induced HI in two probands, and characterize the clinical course. Research Design and Methods: We analyzed HI in two probands and characterized the course of clinical treatment in each, as well as properties of mutant KATP channels expressed in COSm6 cells using Rb efflux and patch-clamp methods. Results: We identified mutation V290M in the pore-forming Kir6.2 subunit in each proband. In vitro expression in COSm6 cells supports the mutation resulting in an inactivating phenotype, which leads to significantly reduced activity in intact cells when expressed homomerically, and to a lesser extent when expressed heteromerically with WT subunits. In one heterozygous proband, fluoro-DOPA scan revealed a causal focal lesion, indicating uniparental disomy with loss of heterozygosity. In a second family, the proband, homozygous for the mutation, was diagnosed with severe diazoxide-unresponsive hypersinsulinism at 2 weeks of age. The patient continues to be treated successfully with octreotide and amlodipine. The parents and a male sibling are heterozygous carriers without overt clinical HI. Interestingly, both the mother and the sibling exhibit evidence of abnormally enhanced glucose tolerance. Conclusions: V290M results in inactivating KATP channels that underlies HI. Homozygous individuals may be managed medically, without pancreatectomy. Heterozygous carriers also show evidence of enhanced glucose sensitivity, consistent with incomplete loss of KATP channel activity.