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Randomised controlled trial of tyrosine supplementation on neuropsychological performance in phenylketonuria
M L Smith1, W B Hanley, J T Clarke
1Department of Psychology, University of Toronto, Mississauga, Ontario, Canada. smithml@psych.utoronto.ca
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.