Kuvan Therapy in Phenylketonuria (PKU): The Effect of Blood Phenylalanine Concentration on Kuvan Response

Kuvan Therapy in Phenylketonuria (PKU): The Effect of Blood Phenylalanine Concentration on Kuvan Response

The investigators will investigate the effect of blood phenylalanine on Kuvan responsiveness in the same patients with PKU when their blood phenylalanine concentrations are altered by diet.

Lowering blood phenylalanine concentrations in Kuvan non-responsive patients with PKU will increase the frequency of Kuvan responsiveness.

Inclusion Criteria:

• all patients with a diagnosis of phenylketonuria
• patients who are over the age of 4 years,
• patients with a fasting blood phenylalanine ≥600µmol/l

Exclusion Criteria:

• female patients who are pregnant or attempting to become pregnant
• children under four years of age
• Concurrent disease of condition that would interfere with study participation or safety such as history of neurological compromise or major medical, psychiatric or learning disorder unrelated to PKU
• Any condition that, in the view of the Investigators, places subject at high risk of poor treatment compliance or of not completing the study
• Use of L-Dopa, methotrexate, or other drugs that may inhibit folate metabolism