Behavioural effects of phenylalanine-free amino acid tablet supplementation in intellectually disabled adults with untreated phenylketonuria

AIM: To evaluate the effects of phenylalanine (Phe)-free essential amino acid (AA) tablets enriched in tyrosine and tryptophan on the performance of intellectually disabled adult patients with untreated phenylketonuria (PKU).

METHODS: Phe-free AA tablets and placebo tablets were administered to 19 untreated PKU subjects on a normal diet for 6 mo in a prospective double-blinded crossover study. The adaptive behaviour of the patients was tested prior to the study and at 6 and 12 mo after the start, using a simplified version of the Vineland Adaptive Behaviour Scale. For each sub-domain, the patients were rated either "0" (for poor performance) or "1" (for good performance). Neurological signs and symptoms and specific behavioural characteristics were recorded monthly by caretakers. Every 6 mo, neurological examination of the patients was performed, and the caretakers were interviewed. The statistical significance of the results was tested by means of the Fisher's exact and Wilcoxon tests.

RESULTS: The most significant changes were an improved concentration and the development of a meaningful smile, which were observed in 44% and 43% of the patients on AA tablet treatment, respectively, but not patients on placebo. Other important but less significant changes included increased awareness of external stimuli (63%) and less self-injury (43%), and 40% were smiling and laughing occasionally. The mean overall rating increased from an initial value of 6.3 to 10.1 in patients when on AA tablet treatment (p=0.002), and to 7.0 in patients when on placebo (p=0.068). The difference between active AA treatment and placebo was statistically significant (p=0.027).

CONCLUSIONS: This pilot study suggests that Phe-free AA tablets enriched in tyrosine and tryptophan may improve the quality of life in some intellectually disabled adults with untreated PKU.