A novel case of compound heterozygous congenital hyperinsulinism without high insulin levels

Cassandra Brady, Andrew A. Palladino, Iris Gutmark-Little

Congenital hyperinsulinism leads to unregulated insulin secretion and hypoglycemia. Diagnosis can be difficult and genetic testing may be warranted. This patient initially presented at 11 months with seizure activity secondary to severe hypoglycemia. Her diagnostic evaluation included genetic studies, which confirmed congenital hyperinsulinism. A novel combination of mutations in the ABCC8 gene leading to diffuse, diazoxide-unresponsive congenital hyperinsulinism was identified. Mutation analysis of ABCC8 showed three variants (R1215W - paternal, pathogenic; W739C - maternal, variant of unknown significance; R1393L - maternal, variant of unknown significance). Her clinical course continues to be complicated by severe, refractory hypoglycemia at age 3 years. We describe a novel compound heterozygous mutation leading to diffuse, diazoxide-unresponsive congenital hyperinsulinism. This case illustrates challenges associated with diagnosing and managing congenital hyperinsulinism and the importance of genetic testing.