Background Tetrahydrobiopterin (BH4)-sensitive phenylketonuria (PKU) can be treated with sapropterin dihydrochloride. We studied metabolic control and health-related quality of life (HRQoL) in PKU patients treated with BH4. Subjects and methods Based on the review of neonatal BH4 test results and mutation analysis in 41 PKU patients, 19 were identified as potentially BH4-sensitive (9 females, 10 males, age 4–18 years). We analyzed phenylalanine (phe) concentrations in dried blood samples, nutrition protocols, and HRQoL questionnaires (KINDL®) beginning from 1 year before, during the first 42 days, and after 3 months of BH4 therapy. Results Eight BH4-sensitive patients increased their phe tolerance (629±476 vs. 2131±1084 mg, p00.006) while maintaining good metabolic control (phe concentration in dried blood 283±145 vs. 304±136 μM, p01.0). Six of them were able to stop dietary protein restriction entirely. BH4- sensitive patients had average HRQoL scores that were comparable to age-matched healthy children. There was no improvement in HRQoL scores after replacing classic dietary treatment with BH4 supply, although personal reports given by the patients and their parents suggest that available questionnaires are inappropriate to detect aspects relevant to inborn metabolic disorders. Discussion BH4 can allow PKU patients to increase their phe consumption significantly or even stop dietary protein restrictions. Unexpectedly, this does not improve HRQoL as assessed with KINDL®, partly due to high scores even before BH4 therapy. Specific questionnaires should be developed for inborn metabolic disorders.

Background Tetrahydrobiopterin (BH4)-sensitive phenylketonuria (PKU) can be treated with sapropterin dihydrochloride. We studied metabolic control and health-related quality of life (HRQoL) in PKU patients treated with BH4. Subjects and methods Based on the review of neonatal BH4 test results and mutation analysis in 41 PKU patients, 19 were identified as potentially BH4-sensitive (9 females, 10 males, age 4–18 years). We analyzed phenylalanine (phe) concentrations in dried blood samples, nutrition protocols, and HRQoL questionnaires (KINDL®) beginning from 1 year before, during the first 42 days, and after 3 months of BH4 therapy. Results Eight BH4-sensitive patients increased their phe tolerance (629±476 vs. 2131±1084 mg, p00.006) while maintaining good metabolic control (phe concentration in dried blood 283±145 vs. 304±136 μM, p01.0). Six of them were able to stop dietary protein restriction entirely. BH4- sensitive patients had average HRQoL scores that were comparable to age-matched healthy children. There was no improvement in HRQoL scores after replacing classic dietary treatment with BH4 supply, although personal reports given by the patients and their parents suggest that available questionnaires are inappropriate to detect aspects relevant to inborn metabolic disorders. Discussion BH4 can allow PKU patients to increase their phe consumption significantly or even stop dietary protein restrictions. Unexpectedly, this does not improve HRQoL as assessed with KINDL®, partly due to high scores even before BH4 therapy. Specific questionnaires should be developed for inborn metabolic disorders.