Tetrahydrobiopterin responsiveness of patients with phenylalanine hydroxylase deficiency [Responsividade à tetrahidrobiopterina em pacientes com deficiência de fenilalanina hidroxilase]

Objective: to identify patients responsive to tetrahydrobiopterin (bh 4) in a sample of brazilians with hyperphenylalaninemia due to phenylalanine hydroxylase deficiency (hpa-pah). methods: interventional study,convenience sampling. the inclusion criteria were: diagnosis of hpa-pah; age ≥ 7 years; phenylalanine-restricted diet and phenylalanine (phe) levels ≥ 6 mg/dl in all blood tests 1 year before inclusion. blood samples were obtained the day before (day 1) and at 0,4,8 (day 2) and 24 h (day 3) after bh 4 intake. phe levels were measured using tandem mass spectrometry. the criteria used to define responsiveness to bh 4 were: criterion 1- phe reduction ≥ 30% 8 h after bh 4 administration; criterion 2 - phe reduction ≥ 30% 24 h after bh 4 administration. results: eighteen patients were enrolled (median age,14 years; 12 boys). five patients were responsive to bh 4,3 according to both criteria (one classical pku,two mild pku); and two according to criterion 2 (one classical pku; one indefinite pku type). there were no differences between phe serum levels on day 1 and at the other time points (p = 0.523). however,phe levels on days 1 and 2 were significantly different (p = 0.006). the analysis of the phenotype-genotype association confirmed its multifactorial character. conclusion: a relevant number of brazilian patients with hpa-pah are responsive to bh4,in agreement with other studies in the literature. copyright © 2011 by sociedade brasileira de pediatria.