SAT165 A Novel Mutation In The HNF4α Gene (C.691C>T, P.arg231trp) Likely To Be Pathogenic For Maturity Onset Diabetes Of The Young Type 1 Presenting With Hyperinsulinemic Hypoglycemia In An Infant

Disclosure: A. Rodriguez: None. S. Sastry: None. W. Chemaitilly: None. N. Gurtunca: None. Background: Maturity Onset Diabetes of the Young type 1 (MODY 1) is a monogenic form of diabetes mellitus caused by a defective HNF4α gene, resulting in reduced insulin secretion and diabetes in early adolescence and young adulthood. MODY 1 is also known to be associated with increased insulin secretion during fetal, neonatal and childhood periods with consequences that range from fetal macrosomia to persistent hyperinsulinism. Traditionally, HNF4α gene mutations represents 5% of all cases of diazoxide-responsive hyperinsulinism. Clinical Case: A 1 month old male born full term and large for gestational age (birth weight of 4920g) following an uncomplicated pregnancy and delivery developed hypoglycemia soon after birth and required hospital admission on day of life 2 with a serum glucose of 30 mg/dL and an insulin level of 5 uIU/mL. A fasting challenge showed hypoglycemia at 9 hours with a serum glucose of 47 mg/dL and an insulin level of 10.3 uIU/mL confirming hyperinsulinemic hypoglycemia. He was started on diazoxide to which he responded well and was placed on a continuous glucose monitor (CGM). He was originally started on diazoxide 8mg/kg/day that later was decreased to 6.6mg/kg/day due to blood glucoses in the 200’s. He passed the fasting study 5 days after starting diazoxide and went home with the CGM with subsequent dose titration made with guidance from remote data sharing. A neonatal hypoglycemia panel was sent and showed a novel mutation, c.691C>T, p.ARG231Trp in the HNF4α gene classified as a variant of uncertain significance. Computer modeling software suggested that this gene might disrupts the gene structure and function. This variant is present in population databases at a 0.0009% frequency and this missense change has been observed in individuals with clinical features of maturity onset diabetes of the young. Patient’s father carries the same mutation and paternal grandmother carries a diagnosis of type 2 diabetes mellitus. Conclusion: This is a novel mutation that should be considered pathogenic based on this patient’s neonatal presentation and previous literature. This case also presents possible uses of CGM in infants with diazoxide responsive congenital hyperinsulinism in order to decrease burden from monitoring and streamline communication with the medical team Presentation: Saturday, June 17, 2023