Header

UZH-Logo

Maintenance Infos

Tetrahydrobiopterin responsiveness in phenylketonuria: prediction with the 48-hour loading test and genotype


Anjema, Karen; van Rijn, Margreet; Hofstede, Floris C; Bosch, Annet M; Hollak, Carla Em; Rubio-Gozalbo, Estela; de Vries, Maaike C; Janssen, Mirian Ch; Boelen, Carolien Ca; Burgerhof, Johannes Gm; Blau, Nenad; Heiner-Fokkema, M Rebecca; van Spronsen, Francjan J (2013). Tetrahydrobiopterin responsiveness in phenylketonuria: prediction with the 48-hour loading test and genotype. Orphanet Journal of Rare Diseases, 8:103.

Abstract

BACKGROUND: How to efficiently diagnose tetrahydrobiopterin (BH4) responsiveness in patients with phenylketonuria remains unclear. This study investigated the positive predictive value (PPV) of the 48-hour BH4 loading test and the additional value of genotype. METHODS: Data of the 48-hour BH4 loading test (20 mg BH4/kg/day) were collected at six Dutch university hospitals. Patients with >=30% phenylalanine reduction at >=1 time points during the 48 hours (potential responders) were invited for the BH4 extension phase, designed to establish true-positive BH4 responsiveness. This is defined as long-term >=30% reduction in mean phenylalanine concentration and/or >=4 g/day and/or >=50% increase of natural protein intake. Genotype was collected if available. RESULTS: 177/183 patients successfully completed the 48-hour BH4 loading test. 80/177 were potential responders and 67/80 completed the BH4 extension phase. In 58/67 true-positive BH4 responsiveness was confirmed (PPV 87%). The genotype was available for 120/177 patients. 41/44 patients with >=1 mutation associated with long-term BH4 responsiveness showed potential BH4 responsiveness in the 48-hour test and 34/41 completed the BH4 extension phase. In 33/34 true-positive BH4 responsiveness was confirmed. 4/40 patients with two known putative null mutations were potential responders; 2/4 performed the BH4 extension phase but showed no true-positive BH4 responsiveness. CONCLUSIONS: The 48-hour BH4 loading test in combination with a classified genotype is a good parameter in predicting true-positive BH4 responsiveness. We propose assessing genotype first, particularly in the neonatal period. Patients with two known putative null mutations can be excluded from BH4 testing.

Abstract

BACKGROUND: How to efficiently diagnose tetrahydrobiopterin (BH4) responsiveness in patients with phenylketonuria remains unclear. This study investigated the positive predictive value (PPV) of the 48-hour BH4 loading test and the additional value of genotype. METHODS: Data of the 48-hour BH4 loading test (20 mg BH4/kg/day) were collected at six Dutch university hospitals. Patients with >=30% phenylalanine reduction at >=1 time points during the 48 hours (potential responders) were invited for the BH4 extension phase, designed to establish true-positive BH4 responsiveness. This is defined as long-term >=30% reduction in mean phenylalanine concentration and/or >=4 g/day and/or >=50% increase of natural protein intake. Genotype was collected if available. RESULTS: 177/183 patients successfully completed the 48-hour BH4 loading test. 80/177 were potential responders and 67/80 completed the BH4 extension phase. In 58/67 true-positive BH4 responsiveness was confirmed (PPV 87%). The genotype was available for 120/177 patients. 41/44 patients with >=1 mutation associated with long-term BH4 responsiveness showed potential BH4 responsiveness in the 48-hour test and 34/41 completed the BH4 extension phase. In 33/34 true-positive BH4 responsiveness was confirmed. 4/40 patients with two known putative null mutations were potential responders; 2/4 performed the BH4 extension phase but showed no true-positive BH4 responsiveness. CONCLUSIONS: The 48-hour BH4 loading test in combination with a classified genotype is a good parameter in predicting true-positive BH4 responsiveness. We propose assessing genotype first, particularly in the neonatal period. Patients with two known putative null mutations can be excluded from BH4 testing.

Statistics

Citations

Dimensions.ai Metrics
12 citations in Web of Science®
14 citations in Scopus®
16 citations in Microsoft Academic
Google Scholar™

Altmetrics

Downloads

102 downloads since deposited on 10 Feb 2014
18 downloads since 12 months
Detailed statistics

Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Children's Hospital Zurich > Medical Clinic
Dewey Decimal Classification:610 Medicine & health
Language:English
Date:2013
Deposited On:10 Feb 2014 09:53
Last Modified:16 Feb 2018 19:24
Publisher:BioMed Central
ISSN:1750-1172
OA Status:Gold
Free access at:PubMed ID. An embargo period may apply.
Publisher DOI:https://doi.org/10.1186/1750-1172-8-103
PubMed ID:23842451

Download

Download PDF  'Tetrahydrobiopterin responsiveness in phenylketonuria: prediction with the 48-hour loading test and genotype'.
Preview
Content: Published Version
Filetype: PDF
Size: 524kB
View at publisher
Licence: Creative Commons: Attribution 2.0 Generic (CC BY 2.0)