ABSTRACT
Abstract Methylmalonic acidemia (MMA) should be diagnosed in early infancy and receive appropriate management promptly after the diagnosis to prevent severe complications leading to death. At present, a newborn screening (NBS) method using tandem mass spectrometry (MS/MS) identifies suspected patients with MMA by elevated propionylcarnitine. In addition, a liquid chromatography tandem mass spectrometry (LC/MS/MS) method using dried blood spot is effective to detect some metabolites as a second-tier test, and reduces the false-positive rate in NBS. However, these tests were only used in screening, and not applied as an examination for evaluating treatment. Herein, we describe a 57-day-old girl with MMA under treatment with cobalamin who had elevated urinary methylmalonic acid levels. We applied the LC/MS/MS method with a separation column to evaluate her cobalamin responsiveness, and discovered an insufficient cobalamin dose earlier than would have been possible using other methods. Based on the current data, this method seems to be applicable for the follow-up of the treatment of MMA patients. However, this should be confirmed with more experience with a larger number of cases and a wider spectrum of disorders.