Summary

Medium-chain acyl-Coenzyme A dehydrogenase deficiency (MCADD) is a disorder of fatty acid β oxidation inherited in an autosomal recessive manner. The enzyme is useful in hepatic ketogenesis, a major source of energy once hepatic glycogen stores become depleted during prolonged fasting. It is a cause of hypoketotic hypoglycaemia in a previously well child. MCADD is not part of newborn screening in Ireland; children are likely to be missed if routine hypoglycaemic screen is not instituted when blood glucose level is below 2.6 mmol/L. This is a case of an otherwise healthy 23-month-old baby girl who presented with severe hypoglycaemia with some initial diagnostic dilemma.