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.

Inclusion Criteria:

• Adult or pediatric subject (no age limit) of either gender with HPA due to PKU or BH4 deficiency.
• Have been shown to be responsive to BH4 or Kuvan. (Note: For Spain only-Have been shown to be responsive to BH4 or for the newly diagnosed subjects to be responsive to Kuvan as defined in the Summary of Product Characteristics [SmPC]).
• Currently being treated with Kuvan® at a participating centre.
• Subject or parent/legal guardian willing and able to provide written signed informed consent and given before any data collection. If a child is old enough to read and write, a separate assent form will be given.

Exclusion Criteria:

• Known hypersensitivity to Kuvan®
• Legal incapacity or limited legal capacity without legal guardian representation
• Breast-feeding

All subjects with HPA due to PKU or BH4 deficiency followed at participating centres.

And specific groups (elderly, pediatric, pregnant women and subjects with renal or hepatic insufficiency).