Long-Term Tetrahydrobiopterin Treatment in PKU Patients of 0-18 Years - Study on Phenylalanine Tolerance and Safety

Inclusion Criteria: * Female and male patients, aged 0-18 years * Phenylalanine-4-hydroxylase (PAH) deficiency shown by mutation analysis * Blood phenylalanine concentration in the target range under dietary treatment * Written consent of a parent or legal representative * Assumed availability within the period of study participation * Patients/parents willing and able to follow the recommended diet * Use of an effective method of contraception in female patients of child bearing potential Exclusion Criteria: * BH4-deficiency due to genetic disorders in biosynthesis or recycling of BH4 * History or current evidence of poor diet compliance * History or current evidence of clinically relevant allergic or idiosyncratic reactions to drugs or food * History of allergic reactions to BH4 or its excipients * Positive pregnancy test (ß-HCG in serum) and lactating females * Participation in other drug trials within the last 30 days before start for the study