Medium Chain Acyl-CoA Dehydrogenase Deficiency; an Unexpected Cause of Neonatal Ketoacidosis.

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) classically presents with hypoketotic hypoglycaemia; however, this presentation is now rare following the introduction of newborn screening. While children with MCADD may produce some ketones, severe ketoacidosis has not been previously described. Here we report two patients with MCADD presenting with severe ketoacidosis in the neonatal period prior to results of newborn screening. Patient 1 presented on Day 5 with hypoglycaemia, profound ketoacidosis and circulatory shock, and developed refractory ventricular tachycardia requiring extra-corporeal membrane oxygenation. Patient 2 presented on Day 4 with severe ketoacidosis, but only borderline hypoglycaemia. The diagnosis of MCADD was rapidly confirmed in both by analysis of acylcarnitines and urine organic acids, with subsequent genetic confirmation of ACADM mutations. We conclude that MCADD should be included in the differential diagnosis of neonatal ketoacidosis, with or without hypoglycaemia.