Urine Phenylacetylglutamine Determination in Patients with Hyperphenylalaninemia

Phenylketonuria (PKU), an autosomal-recessive inborn error of phenylalanine (Phe) metabolism is the most prevalent disorder of amino acid metabolism. Currently, clinical follow-up relies on frequent monitoring of Phe levels in blood. We hypothesize that the urine level of phenylacetylglutamine (PAG), a phenyl-group marker, could be used as a non-invasive biomarker. In this cross-sectional study, a validated liquid chromatography coupled to tandem mass spectrometry (LC-MS) method was used for urinary PAG quantification in 35 participants with hyperphenylalaninemia (HPA) and 33 age- and sex-matched healthy controls. We have found that (a) PKU patients present higher urine PAG levels than healthy control subjects, and that (b) there is a significant correlation between urine PAG and circulating Phe levels in patients with HPA. In addition, we show a significant strong correlation between Phe levels from venous blood samples and from capillary finger-prick dried blood spot (DBS) samples collected at the same time in patients with HPA. Further research in order to assess the potential role of urine PAG as a non-invasive biomarker in PKU is warranted.Funding: J.d.l.H. acknowledges the Biocruces Bizkaia Health Research Institute contract for Intensification of Research Activities. This work was partially funded by the Basque Department of Education (IT1281-19). The chemical analysis and the preparation of the manuscript were partially financed by Biocruces Bizkaia Health Research Institute and Carlos III Health Research Institutes. Acknowledgments: The authors thank the patients with hyperphenylalaninemia and healthy volunteers for their kind participation. We thank the Association for those affected by phenylketonuria of the Basque Country (Euskadi PKU-OTM Elkartea) for their collaboration. J.d.l.H., L.C., N.L.-O., G.F., A.A. and M.U. are members of the European Reference Network for Rare Hereditary Metabolic Disorders (MetabERN)—Project ID No. 739543