Benchmark Examination of Blood Amino Acids Patterns in Phenylketonuria Neonates and Young Children on Phenylalanine-Restricted Dietary Treatment.

Phenylalanine-restricted diets have been the basis of therapy for phenylketonuria; however, little is known how this treatment effects homeostasis of other amino acids. This study aimed to assess blood amino acid alterations in phenylketonuric neonates before and after treatment to identify any residual amino acid alterations with phenylalanine restriction in these treated children. Concentrations of 11 amino acids were measured using liquid chromatography-tandem mass spectrometry performed on dried blood spots. Elevated blood phenylalanine, arginine, citrulline, valine, methionine concentrations and decreased tyrosine, proline concentrations were observed in phenylketonuria neonates relative to controls, of which phenylalanine, arginine, methionine, tyrosine, and proline levels could be either partially or completely restored with dietary intervention, whereas citrulline and valine were not restored and remained higher. Blood amino acid homeostasis is disrupted in phenylketonuria. Although dietary intervention adjusts amino acid homeostasis in the direction of a healthy equilibrium, complete restoration is not achieved.