Neonatal acidosis associated with transient methylmalonicaciduria and vitamin B12 deficiency.

Investigation of a neonate presenting with a metabolic acidosis, vomiting and an apnoeic attack revealed abnormal urinary excretion of methylmalonic acid (MMA) associated with a low serum vitamin B12. Restriction of dietary protein was followed by normalisation of acid-base balance. Reintroduction of normal daily protein intake did not precipitate flrther acidosis or increased excretion of MMA. The transient methylmalonicaciduria was probably due to deficiency of vitamin B12.