Randomised controlled trial of tyrosine supplementation on neuropsychological performance in phenylketonuria

Abstract

Objective: To test the efficacy of tyrosine supplementation, as an adjunct to dietary treatment, on neuropsychological test performance in individuals with phenylketonuria.

Design: A randomised controlled trial of tyrosine supplementation using a double blind crossover procedure with three four week phases.

Setting: The Hospital for Sick Children, Toronto.

Participants: 21 individuals with phenylketonuria (ages 6 to 28 years, mean 11.3).

Intervention: Participants were given 100 mg/kg body weight/d of L-tyrosine or L-alanine (placebo).

Results: At baseline, performance on several of the neuropsychological test measures was correlated with tyrosine levels. Dietary supplements of tyrosine increased plasma tyrosine concentrations; however, no change in test performance was found across the tyrosine and placebo phases of the study.

Conclusions: Tyrosine supplementation of this type does not appear to alter neuropsychological performance in individuals with phenylketonuria.