Observational Study on the Long Term Safety of Kuvan® Treatment in Patients With Hyperphenylalaninemia (HPA) Due to Phenylketonuria (PKU) or BH4 Deficiency

Kuvan® is a synthetic copy of a body's own substance called tetrahydrobiopterin (BH4). BH4 is required by the body to use an amino acid called phenylalanine in order to build another substance called tyrosine. Kuvan® received marketed authorisation in Europe in December 2008 and is now available in several European countries for the treatment of Hyperphenylalaninemia (HPA). The primary objective is to assess the long-term safety in subjects treated with Kuvan®. Secondary objectives are to provide additional information regarding: * Safety in specific subject groups (elderly, pediatric, pregnant women and subjects with renal or hepatic insufficiency). * Growth and neurocognitive outcomes for subjects with hyperphenylalaninemia (HPA) who are receiving treatment with Kuvan®. * Progress and outcome of pregnancy for women with HPA who become pregnant while receiving treatment with Kuvan® (these women will be enrolled in a dedicated sub-registry). * Assessment of adherence to diet and to Kuvan®. * Assessment of long-term sensitivity to Kuvan®treatment.

This is an observational, multicenter, drug registry Study. The study will have a total duration of 15 years, including a 10-year inclusion period. No diagnostic, therapeutic or experimental intervention is involved. Subjects will receive clinical assessments, medications and treatments solely as determined by their study physician.