Dietary management of inborn errors of amino acid metabolism with protein-modified diets

This paper presents experiences encountered with protein-modified diets (PMD) in the management of 67 patients, aged 1 day to 14 years, followed in the Pediatric Nutrition Clinic in the past 5 years. All had inborn errors of amino acid metabolism: maple syrup urine disease (MSUD), 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase deficiency, propionic acidemia (PPA), or methylmalonic aciduria (MMA). In early infancy, the diet prescription is frequently adjusted to search for the infant's tolerance level of restricted amino acids. The levels must be established when natural foods other than milk are added to the PMD. The amino acids restricted are leucine, isoleucine, and valine in MSUD; leucine in HMG-CoA lyase deficiency; and isoleucine, methionine, threonine, and valine in PPA and MMA. Efficacy of the PMD depends on accuracy in prediction of the restricted amino acid requirement and the willingness and ability of parents and patients to conform to its demands.