Vitamin E Efficacy in HI/HA

Congenital hyperinsulinism (HI) is a rare disorder of pancreatic beta cell insulin secretion that causes persistent and severe hypoglycemia starting at birth. Hyperinsulinism/hyperammonemia (HI/HA) syndrome is the second most common type of congenital HI and is caused by activating mutations in glutamate dehydrogenase (GDH). Patients with HI/HA exhibit fasting hyperinsulinemic hypoglycemia, protein-induced hypoglycemia, hyperammonemia, seizures, and intellectual disability independent of hypoglycemia. These effects result from abnormal GDH activity in the beta cells, liver and kidney cells, neurons, and astrocytes. The only available treatment for HI/HA syndrome is diazoxide, which acts on the beta cells to decrease insulin secretion but has no effect on GDH activity itself or on other cell types. Thus, there remains a significant unmet need for improved therapies for this disorder. Pre-clinical data show that vitamin E inhibits GDH activity in human cell lines and improves fasting hypoglycemia in a GDH HI mouse model. Pilot study data show that vitamin E supplementation with a moderate dose is well-tolerated in children and adults with HI/HA syndrome, while continuing diazoxide treatment. However, most subjects continued to exhibit protein-induced hyperinsulinemic hypoglycemia. We hypothesize that a higher vitamin E dose will inhibit GDH over-activity in subjects with HI/HA syndrome, resulting in improved hyperinsulinemic hypoglycemia, reduced blood ammonia concentration, and decreased seizure activity.