Novel Hypoglycemia Phenotype in Congenital Hyperinsulinism Due to Dominant Mutations of Uncoupling Protein 2

The rarest genetic form of congenital hyperinsulinism (HI) has been associated with dominant inactivating mutations in uncoupling protein 2 (UCP2), a mitochondrial inner membrane carrier that modulates oxidation of glucose vs amino acids.

To evaluate the frequency of UCP2 mutations in children with HI and phenotypic features of this form of HI.

We examined 211 children with diazoxide-responsive HI seen at The Children's Hospital of Philadelphia (CHOP) between 1997 and October 2016.

CHOP Clinical and Translational Research Center.

Of 211 cases of diazoxide-responsive HI, we identified 5 unrelated children with UCP2 mutations (5 of 211; 2.4%). All 5 were diagnosed with HI before 6 months of age; diazoxide treatment was only partly effective in 3 of the 5. Among the 5 cases, 4 unique mutations (3 missense and 1 splicing) were identified. Three mutations were novel; 1 was previously reported. In vitro functional assays showed 30% to 75% decrease in UCP2 activity. Two of the children, when not taking diazoxide, developed hypoketotic-hypoglycemia after fasting 15 to 20 hours; a similar trend toward hypoglycemia after fasting 24 hours occurred in 4 adult carriers. In contrast, both children and 2 of the 4 carriers developed symptomatic hypoglycemia 4 hours following oral glucose. Unusual oscillating glucose and insulin responses to oral glucose were seen in both cases and carriers.

These data indicate that dominant UCP2 mutations are a more important cause of HI than has been recognized and that affected individuals are markedly hypersensitive to glucose-induced hypoglycemia.