Paired-Like Homeobox 2B (PHOX2B) Mutation and the Hidden Endocrine Puzzle: Hyperinsulinism in Congenital Central Hypoventilation Syndrome.

Congenital central hypoventilation syndrome (CCHS) is a rare disorder of autonomic control of breathing caused predominantly by paired-like homeobox 2B (PHOX2B) mutations and frequently accompanied by broader autonomic dysfunction affecting cardiovascular, gastrointestinal, and endocrine systems. We report a four-month-old female with genetically confirmed PHOX2B polyalanine repeat expansion (c.726_764dup; p.Ala248_Ala260dup; 33 repeats) who developed recurrent, symptomatic postprandial hypoglycemia after transitioning from continuous enteral feeding to oral bolus feeds. Critical samples during hypoglycemia (blood sugar nadir 26 mg/dL) showed inappropriately elevated insulin and C-peptide with suppressed ketones and appropriate cortisol and growth hormone (GH) responses, while metabolic work-up was otherwise unremarkable. The pattern supported reactive postprandial hyperinsulinemic hypoglycemia due to autonomic dysregulation rather than congenital hyperinsulinism. Glycemic stability was achieved by reinstating slow, continuous feeds and avoiding rapid carbohydrate boluses; dextrose boluses precipitated rebound hypoglycemia. The case underscores an under-recognized endocrine manifestation of PHOX2B-related CCHS and highlights practical management-continuous/slow feeding, cautious use of dextrose, and multidisciplinary follow-up to maintain euglycemia during feeding transitions.