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

Authors


Flemming Güttler, The John F. Kennedy Institute, Department of Inherited Metabolic Diseases and Molecular Genetics, Gl. Landevej 7 DK-2600 Ankara Denmark +45 43 26 01 00 +45 43 43 11 30 flg@kennedy.dk

Abstract

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.

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