Challenging diagnosis of congenital hyperinsulinism in two infants of diabetic mothers with rare pathogenic KCNJ11 and HNF4A gene variants

Congenital hyperinsulinism (CHI) is the leading cause of persistent hypoglycemia in infants. The infants of diabetic mothers (IDMs) very frequently present with neonatal hypoglycemia associated to transient hyperinsulinism however the incidence of CHI in IDMs is unknown. Here we report 2 cases of CHI where the diagnoses were challenged and delayed because both patients were infants of diabetic mothers (IDMs) and had concomitant complicated medical conditions. Case 1 was heterozygous for a likely pathogenic variant in KCNJ11 (p.Arg206Cys), and Case 2 was heterozygous for a pathogenic HNF4A variant, (p.Arg267Cys). HNF4A -associated CHI is very rare, and this particular case had a clinical phenotype quite different from that of previously described HNF4A -CHI cases. This case series is one of few reports in the medical literature describing two IDMs with persistent recurrent hypoglycemia secondary to CHI, and a different clinical phenotype for HNF4A -associated CHI. IDMs typically present with transient hyperinsulinism lasting no more than 2–3 days. Since being an IDM does not exclude CHI, this diagnosis should always be considered as the mostly likely etiology if neonatal hypoglycemia persists longer than the described time frame and genetic testing for CHI confirmation is highly suggested.