Vitamin E Supplementation in Hyperinsulinism/Hyperammonemia Syndrome

Inclusion Criteria: * Individuals age ≥12 months and ≤40 years * Diagnosis of HI/HA syndrome * On diazoxide therapy for treatment of hypoglycemia * Females ≥11 years of age or menstruating must have a negative urine/serum pregnancy test and must use an acceptable method of contraception, including abstinence, a barrier method (diaphragm or condom), Depo-Provera, or an oral contraceptive, for the duration of the study. * Informed consent for participants ≥18 years. Parental/guardian permission (informed consent) and, if appropriate, child assent for participants \<18 years. Exclusion Criteria: * Individuals age \<12 months or \>40 years * Individuals who have experienced an allergic reaction to Vitamin E * Individuals with a known allergy to dairy, whey, or soy * On concurrent therapy with a medication known to be metabolized by the CYP3A pathway * Individuals with a known increased risk of bleeding (bleeding disorder or on antiplatelet or anticoagulation therapy) * Vitamin E supplementation within 30 days prior to enrollment, including multivitamins containing Vitamin E * Severe hypoglycemia (plasma glucose \<50 mg/dL on repeat checks using home glucose meter) more than once weekly within 30 days prior to enrollment. * Evidence of a medical condition that might alter results or compromise the interpretation of results, including active infection, kidney failure, severe liver dysfunction, severe respiratory or cardiac failure. * Evidence of severe hematologic abnormality including severe anemia and/or thrombocytopenia. * Any investigational drug use within 30 days prior to enrollment. * Pregnant or lactating females. * Parents/guardians or subjects who, in the opinion of the Investigator, may be non-compliant with study schedules or procedures. * Unable to provide informed consent (e.g. impaired cognition or judgment). * Parents/guardians or subjects with limited English proficiency.