Abstract
Early nutritional therapy of phenylketonuria (PKU) has been successful in preventing the severe neurological consequences of high plasma phenylalanine levels, resulting in individuals with PKU achieving cognitive ability in the normal or near-normal range. However, neuropsychological and nutritional deficits are reported, and the current diet therapy is onerous for some families and particularly adolescents and adults, as it is for late-diagnosed patients. Patient-specific alternative therapies, including large neutral amino acids, glycomacropeptides, tetrahydrobiopterin, phenylalanine ammonia lyase, and gene replacement hold the promise of improving outcome and quality of life.