Background: Sapropterin dihydrochloride, an EMEA-approved synthetic formulation of BH4, has been available in Europe since 2009 for PKU patients older than 4 years, but its use with younger children is allowed in France based on an expert recommendation. We report the cases of 15 patients treated under the age of 4 years and demonstrate the safety and efficacy of this treatment for patients in this age group.
Patients and method: We report the use of BH4 in 15 PKU patients treated before the age of 4 years.
Results: Fifteen patients were enrolled in this retrospective study. Mean phenylalaninemia at diagnosis was 542 ± 164 μM and all patients had mild PKU (maximal phenylalaninemia: 600-1200 μM). BH4 responsiveness was assessed using a 24-hour BH4 loading test (20 mg/kg), performed during the neonatal period (n = 11) or before 18 months of age (n = 4). During the test, these patients exhibited an 80 ± 12% decrease in phenylalaninemia. Long-term BH4 therapy was initiated during the neonatal period (n = 7) or at the age of 13 ± 12 months (n = 8). The median duration of treatment was 23 months [min 7; max 80]. BH4 therapy drastically improved dietary phenylalanine tolerance (456 ± 181 vs 1683 ± 627 mg/day, p < 0.0001) and allowed a phenylalanine-free amino acid mixture to be discontinued or not introduced in 14 patients. Additionally, in the eight patients treated after a few months of diet therapy, BH4 treatment significantly decreased mean phenylalaninemia (352 ± 85 vs 254 ± 64 μM, p < 0.05), raised the percentage of phenylalaninemia tests within therapeutic targets [120-300 μM] (35 ± 25 vs 64 ± 16%, p < 0.05), and reduced phenylalaninemia variance (130 ± 21 vs 93 ± 27 μM, p < 0.05). No side effects were reported.
Conclusion: BH4-therapy is efficient and safe before the age of 4 years in mild PKU, BH4-responsive patients.