Document Detail

Optimized loading test to evaluate responsiveness to tetrahydrobiopterin (BH(4)) in Brazilian patients with phenylalanine hydroxylase deficiency.
MedLine Citation:
PMID:  22014474     Owner:  NLM     Status:  Publisher    
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 ≥4years, and median Phe plasma concentration ≤600μmol/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 27h 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 12yrs; 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.
Tatiéle Nalin; Ingrid Dalira Schweigert Perry; Angela Sitta; Carmen Regla Vargas; Maria Luiza Saraiva-Pereira; Roberto Giugliani; Nenad Blau; Ida Vanessa Doederlein Schwartz
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-9-20
Journal Detail:
Title:  Molecular genetics and metabolism     Volume:  -     ISSN:  1096-7206     ISO Abbreviation:  -     Publication Date:  2011 Sep 
Date Detail:
Created Date:  2011-10-21     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9805456     Medline TA:  Mol Genet Metab     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2011 Elsevier Inc. All rights reserved.
Post-Graduation Program in Medicine: Medical Sciences, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
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