Tetrahydrobiopterin-responsive phenylketonuria: The New South Wales experience

Recent studies have shown that a subgroup of phenylketonuric patients respond to high doses of BH 4 (20 mg/kg) by a decrease of plasma phenylalanine. A clinically significant response has been defined as a decrease in phenylalanine by more than 30% within 24 h, after a BH 4 challenge. We report our experience with 37 patients diagnosed with hyperphenylalaninemia, mild, moderate, or classical Phenylketonuria (PKU) using a seven day combined BH 4 and phenylalanine load. Nine of the 37 patients responded with a 30% decrease in their phenylalanine levels in the first 8 h of treatment. A total of 17 patients (46%) had a decrease of at least 30% during the study period. This study confirms that a significant number of patients with mild to moderate PKU will respond to a BH 4 load. Furthermore, it confirms that the seven-day phenylalanine test is more sensitive in detecting BH 4 responsive patients.