Carnitine Status in Early-Treated Children, Adolescents and Young Adults with Phenylketonuria on Low Phenylalanine Diets

Abstract

Background: In patients with phenylketonuria (PKU), the carnitine status may be impaired for metabolic or dietary reasons, including low carnitine intake, a deficient synthesis and acylcarnitine production from phenylalanine (Phe) metabolites. Methods: Free carnitine and acylcarnitine status was assessed in 30 PKU patients, aged 0.5–36 years, mean age 13.8 years. Our cohort was divided into 2 groups according to the preparations of Phe-free amino acids (AA) prescribed, with or without carnitine supplementation. Daily Phe intake, dosage of AA mixtures and body weight were recorded along with measurements of acylcarnitines in blood spots (by tandem mass spectrometry) and serum AA. Control data were obtained from 50 healthy volunteers (aged 0.2–39 years, mean age 14.2. years). Statistical analysis comprised the t test, ANOVA and Pearson’s correlation. Results: PKU patients had lower free carnitine (C0) concentrations than controls (25.82 ± 7.38 vs. 31.28 ± 6.17 µmol/l; p < 0.001) and lower octanoyl- and decanoylcarnitine. Mean C0 and acylcarnitine concentrations did not differ between PKU patients taking the various protein substitutes with or without carnitine; mean C0 levels in PKU patients receiving AA enriched with carnitine were still lower compared with controls (p < 0.05). Conclusions: Actual dietary regimens can not completely normalize the carnitine status; therefore, carnitine levels should be given careful consideration in subjects with PKU.