Congenital hyperinsulinemic hypoglycaemia in a neonate: a rare homozygous ABCC8 gene mutation.

Hyperinsulinemic hypoglycaemia (HH) is a heterogeneous disorder causing persistent hypoketotic hypoglycaemia in neonates and infants. Congenital hyperinsulinism (CHI) is a rare cause of HH, resulting from inappropriate insulin secretion by pancreatic β-cells due to genetic defects in key genes, notably ABCC8 and KCNJ11, which encode the SUR1 and Kir6.2 components of the K channels, respectively. We present a case of a neonate with congenital HH with persistent hypoglycaemia since birth, which was managed with high-dose glucose infusions, diazoxide and octreotide. A homozygous pathogenic missense variant, c4253G>A (p.Arg1418His) in Exon 35 of the ABCC8 gene was identified in the neonate, confirming CHI. Despite initial refractoriness to treatment, the infant responded to octreotide therapy, cornstarch and careful management with regular feeds and monitoring, avoiding the need for surgical intervention. This case underscores the critical role of genetic diagnosis and timely management in preventing long-term neurological sequelae.