A Novel ABCC8 Variant in an Adult with Hyperinsulinemic Hypoglycemia Suggestive of Congenital Hyperinsulinism: A Case Report.

Background and Clinical Significance: Congenital hyperinsulinism (CHI) is a disorder involving excessive insulin secretion due to mutations in the insulin regulation pathways. Patients are typically diagnosed during infancy following recurrent hypoglycemic events, which may lead to irreversible neurologic damage if left untreated. Adult presentation and diagnosis are rare. Case Presentation: Here, we report the unusual case of a 41-year-old patient who presented with recurrent episodes of hyperinsulinemic hypoglycemia. An extensive diagnostic evaluation yielded no evidence of an acquired cause. Genetic testing revealed a heterozygous novel c.4078G>C substitution in the ABCC8 gene, which plays a role in the insulin secretion pathway. This variant may have been the cause for CHI going unrecognized during the patient's childhood and could have also contributed to his uncontrolled convulsive disorder. Treatment with diazoxide and octreotide led to significant clinical improvement, with no severe hypoglycemic events during the final week of hospitalization. Conclusions: This case emphasizes the importance of considering congenital hyperinsulinism in the differential diagnosis of adult patients evaluated for hyperinsulinemic hypoglycemia, especially when standard workup fails to identify an underlying cause.