The Impact of Frequency of Home Phenylalanine Measurements on Metabolic Control in a Population of Patients With Classic Phenylketonuria

Inclusion criteria

• Informed consent to participate in the study
• Male or female participants aged ≥18 and ≤65 years
• Clinical diagnosis of classic phenylketonuria (PKU) documented in the medical history by at least 2 measurements of blood phenylalanine concentration

≥600 μmol/l and a predicted PAH enzyme activity <1% (GPV), requiring treatment with a low-protein diet supplemented with special low-phenylalanine amino acid mixtures

• Blood phenylalanine concentration in the range of 360-900 μmol/l during current therapy at the time of screening, and blood phenylalanine concentration in the range of 360-900 μmol/L during current treatment, based on the arithmetic mean of the last 3 Phe measurements from the participant's medical history (including the value from the screening)
• Ability and willingness, in the investigator's opinion, to comply with all requirements of the study.

Exclusion criteria

• 1. Patients who have not followed a phenylalanine (Phe)-restricted diet for 6 months prior to the start of the study or who are not willing to continue this diet 2. Phe concentration > 900 μmol/L in any measurement taken within 6 months prior to the start of the study 3. Drug or alcohol abuse 4. A person who, in the investigator's opinion, is unable or unwilling to comply with the study requirements. Persons who are legally incapacitated will not be eligible to participate in the study 5. Current participation in another clinical trial or use of any experimental drug within 30 days prior to screening 6. Planning a pregnancy or being pregnant 7. Confirmed diagnosis of primary BH4 deficiency, documented by the presence of pathogenic mutations in both alleles of the following genes: 6-pyroyl-tetrahydrobiopterin synthase, recessive guanosine triphosphate (GTP) cyclohydrolase, sepiapterin reductase, dihydropteridine quinonoid reductase, or pterin 4 alpha-carbinolamine dehydratase 8. Use of sapropterin, sepiapterin, or pegvaliaza concurrently or within 365 days prior to screening