The purpose of this study is to determine whether adolescent and adult patients with phenylketonuria who are on long-term phenylalanine-restricted diet suffer from endothelial dysfunction.

The aim of the study is the examination of endothelial dysfunction and oxidative stress markers in adolescent and adult patients with phenylketonuria (PKU), in correlation to phenylalanine values und phenylalanine-restricted diet. 25-50 patients with PKU aged ≥16 years of age and a control group of 25 age- and sex-matched healthy volunteers will be included in the study.

Endothelial dysfunction will be measured by venous occlusion plethysmography on the lower legs in the PKU patients and in the control group. Wave velocity, aortic stiffness, and intima media thickness of the common carotid artery will be measured by vicorder and duplex ultrasound scanner in the PKU patients and in the control group. Analyses of phenylalanine metabolites and renal function will be performed only in the PKU patients, analyses of oxidative stress markers in the PKU patients and in the control group. Dietary protocols of the patients with PKU will be calculated for their daily phenylalanine, total protein, and calorie intake. Results of the study will be kept in the medical records and paper case report forms. Data will be analyzed only in pseudonymized form.

Inclusion Criteria:

• phenylketonuria due to phenylalanine hydroxylase deficiency
• age ≥16 years

Exclusion Criteria:

• age <16 years
• pregnancy or maternity
• late-treated phenylketonuria
• phenylketonuria due a defect in BH4 synthesis or BH4 regeneration

Patients aged ≥ 16 years with PKU diagnosed by newborn screening who are followed up in the Metabolic Unit of the Charité University Medical Center Berlin (Interdisciplinary Center for Metabolic Diseases, Dept. of Hepatology and Gastroenterology, as well as Dept. of Pediatric Endocrinology, Gastroenterology and Metabolic Diseases).