Evaluation of branched‐chain amino acid intake in children with maple syrup urine disease and methylmalonic aciduria

Abstract

The biochemical and growth responses to dietary branched-chain amino acid (BCAA) intake were studied in two children; one with a disorder of branched-chain amino acid metabolism, maple syrup urine disease (MSUD) (McKusick 24860), and another with methylmalonic aciduria (MMA) (McKusick 25100). Biochemical control of MSUD focussed on plasma leucine levels while measurement of plasma ammonia levels was used in MMA. From 0 to 2.75 years both patients exhibited five episodes of toxicity. In each case toxicity was associated with dietary indiscretion or infection. The quantity of protein tolerated was always less in the MMA patient and was approximately 1 g/kg/day. From 1 to 2.75 years each patient's growth velocity approximated their predicted growth channel except during periods of toxicity. In both cases leucine intake, which gave normal growth without toxicity, was always judged to be less than the FAO/WHO recommendations. The BCAA intake of the MMA patient was remarkably stable from 0.5 to 2.75 years and at 2 years of age isoleucine and valine intake approximated the FAO/WHO recommendations. From 2 to 2.75 years BCAA intake (mg/kg/day) of the MSUD patient was less than that of the MMA patient and well below FAO/WHO recommendations. Neuromotor development in both patients is normal.