The 48-hour tetrahydrobiopterin loading test in patients with phenylketonuria: evaluation of protocol and influence of baseline phenylalanine concentration.
Mol Genet Metab
; 104 Suppl: S60-3, 2011.
Article
en En
| MEDLINE
| ID: mdl-21996137
ABSTRACT
BACKGROUND:
The 24- and 48-hour tetrahydrobiopterin (BH4) loading test (BLT) performed at a minimum baseline phenylalanine concentration of 400 µmol/l is commonly used to test phenylketonuria patients for BH4 responsiveness. This study aimed to analyze differences between the 24- and 48-hour BLT and the necessity of the 400 µmol/l minimum baseline phenylalanine concentration.METHODS:
Data on 186 phenylketonuria patients were collected. Patients were supplemented with phenylalanine if phenylalanine was <400 µmol/l. BH4 20mg/kg was administered at T = 0 and T = 24. Blood samples were taken at T=0, 8, 16, 24 and 48 h. Responsiveness was defined as ≥ 30% reduction in phenylalanine concentration at ≥ 1 time point.RESULTS:
Eighty-six (46.2%) patients were responsive. Among responders 84% showed a ≥ 30% response at T = 48. Fifty-three percent had their maximal decrease at T = 48. Fourteen patients had ≥ 30% phenylalanine decrease not before T = 48. A ≥ 30% decrease was also seen in patients with phenylalanine concentrations <400 µmol/l.CONCLUSION:
In the 48-hour BLT, T = 48 seems more informative than T = 24. Sampling at T = 32, and T = 40 may have additional value. BH4 responsiveness can also be predicted with baseline blood phenylalanine <400 µmol/l, when the BLT is positive. Therefore, if these results are confirmed by data on long-term BH4 responsiveness, we advise to first perform a BLT without phenylalanine loading and re-test at higher phenylalanine concentrations when no response is seen. Most likely, the 48-hour BLT is a good indicator for BH4 responsiveness, but comparison with long term responsiveness is necessary.
Texto completo:
1
Banco de datos:
MEDLINE
Asunto principal:
Fenilalanina
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Fenilcetonurias
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Biopterinas
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Técnicas y Procedimientos Diagnósticos
Tipo de estudio:
Diagnostic_studies
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Evaluation_studies
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Prognostic_studies
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Risk_factors_studies
Límite:
Adolescent
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Adult
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Child
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Child, preschool
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Female
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Humans
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Infant
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Male
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Middle aged
Idioma:
En
Año:
2011
Tipo del documento:
Article