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Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-56815

Nalin, T; Perry, I D; Sitta, A; Vargas, C R; Saraiva-Pereira, M L; Giugliani, R; Blau, N; Schwartz, I V (2011). Optimized loading test to evaluate responsiveness to tetrahydrobiopterin (BH4) in Brazilian patients with phenylalanine hydroxylase deficiency. Molecular Genetics and Metabolism, 104(Suppl.):S80-S85.

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INTRODUCTION: Recent studies showed that phenylalanine (Phe) plasma concentrations may decrease in some patients with hyperphenylalaninemia (HPA) due to phenylalanine hydroxylase (PAH) deficiency, after the administration of tetrahydrobiopterin (BH(4)). OBJECTIVE: To determine responsiveness to a single dose of BH(4) administered according to an innovative protocol using a combined Phe and BH(4) loading test in Brazilian phenylketonuria (PKU) patients. METHODS: Patient age should be ≥ 4 years, and median Phe plasma concentration ≤ 600 μmol/L when following dietary restrictions. Participants received a simple Phe loading test using 100mg/kg L-Phe (Test 1) and a combined Phe+BH(4) loading test using 100mg/kg L-Phe and 20mg/kg/BH(4) (Test 2). Blood samples were collected at baseline and 3, 11 and 27 h after Phe ingestion (T0, T1, T2 and T3). Responsiveness was defined as: criterion A: plasma Phe reduction of ≥ 30% at T1 and T2 for Tests 1 and 2; criterion B: plasma Phe reduction of ≥ 30% at T1 and T3 for Tests 1 and 2; and criterion C: at least 30% difference of the areas under the Phe curve for Tests 1 and 2. RESULTS: Eighteen patients (median age 12 yrs; 8 classical PKU; 10 mild PKU) participated in the study. Six patients (2 classical PKU; 4 mild PKU) were classified as responsive according to at least one of the criteria. Responsiveness was concordant when criteria A + B we compared with criterion C (kappa = 0.557; p = 0.017). Of the patients whose genotype was available (n = 16), six had data about BH(4)-responsiveness genotypes described in the literature, which were in agreement with our findings. CONCLUSION: The comparison of simple Phe loading and combined Phe + BH(4) loading seems to be an optimal method to evaluate responsiveness to BH(4) in patients with good metabolic control. Copyright © 2011 Elsevier Inc. All rights reserved.


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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Children's Hospital Zurich > Medical Clinic
04 Faculty of Medicine > Center for Integrative Human Physiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Deposited On:28 Jan 2012 16:04
Last Modified:30 Nov 2013 01:35
Publisher DOI:10.1016/j.ymgme.2011.09.019
PubMed ID:22014474

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