• hyperinsulinism
• hypoglycaemia

• BWS, Beckwith-Weidemann syndrome
• EGG, electrogastrogram
• HI, hyperinsulinism
• HOCM, hypertrophic obstructive cardiomyopathy
• OGTT, oral glucose tolerance test

Transient hyperinsulinism (HI) has been reported in infants born to mothers with diabetes mellitus,¹ in infants subjected to perinatal asphyxia, or intrauterine growth restriction,² in those born with Beckwith-Weidemann syndrome (BWS),³ and in those with rhesus haemolytic disease.⁴ The aetiology and mechanisms that underlie transient HI in some of these conditions remain poorly understood. Little is known of the histopathology and membrane physiology of pancreatic β cells in these patients, since the HI is most often transient, not requiring a pancreatectomy. In comparison there has been an explosion of knowledge in the past five years about persistent HI. Mutations in five different genes have been implicated to date.^5,6 These mutations affect the ionic control of insulin secretion from the pancreatic β cell. The most common form of persistent HI is associated with mutations in the SUR1 (ABCC8) and KIR6.2 (KCNJ 11) genes, which cause loss of function of the K_ATP channel in the β cell membrane with unregulated secretion of insulin from the pancreatic β cell.⁵

We report two cases of transient HI associated with macrosomia, severe hypertrophic obstructive cardiomyopathy (HOCM), hepatomegaly, and nephromegaly. One of the babies had evidence of a microcolon. There was a history of mild maternal gestational diabetes requiring no treatment in one patient, while the maternal oral glucose tolerance test in the second patient was normal. These cases represent an atypical form of severe transient HI.