Methylmalonic Acidemia a new inborn error of metabolism which may cause fatal acidosis in the neonatal period

Abstract

A new inborn error of metabolism characterized by severe metabolic acidosis, polyuria, dehydration, emaciation and the urinary excretion of large amounts of methylmalonic acid is described. Two siblings of the patient have died in the neonatal period with clinical symptoms strongly resembling those of our patient. Our studies indicate that the metabolic block is located in the degradation of methylmalonic acid to succinic acid. Valine was shown to be a precursor of methylmalonic acid in accordance with the known metabolic formation of this acid. Small amounts of valine were metabolized to CO₂, suggesting that the metabolic defect is incomplete. The blood concentration, body burden, distribution volume, serum half life and renal clearance of methylmalonic acid were determined. Treatment with cyanocobalamin and with cobamide coenzyme did not appear to influence the course of the disease. A diet low in isoleucine, valine, threonine and methionine significantly reduced the urinary excretion of methylmalonic acid, leading to considerable improvement of the clinical condition with reduction of the tendency to acidosis. However, the patient developed a severe infection, and died of septicemia.