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Phenylalanine loading in pediatric patients with dopa-responsive dystonia: revised test protocol and pediatric cutoff values


Opladen, T; Okun, J G; Burgard, P; Blau, N; Hoffmann, G F (2010). Phenylalanine loading in pediatric patients with dopa-responsive dystonia: revised test protocol and pediatric cutoff values. Journal of Inherited Metabolic Disease, 33(6):697-703.

Abstract

OBJECTIVES: The objectives of this study were to determine the value of phenylalanine (Phe) loading for diagnosing dopa-responsive dystonia (DRD) in children.

METHODS: We investigated orally administered Phe loading tests (100 mg/kg) in seven patients with confirmed DRD and 17 pediatric patients with clinically suspected but excluded DRD. Results of Phe, tyrosine (Tyr), and biopterin from plasma and dried blood spot (DBS) analyses were correlated, and pediatric cutoff values established.

RESULTS: The peak Phe concentration following a Phe load in the pediatric DRD population is lower than reported in adults. By using adult cutoff values and either Phe/Try ratios or biopterin concentrations only, false positive and false negative results are frequent. Only the combined analysis of the Phe/Tyr ratio and biopterin concentration is reliable in children. In children with DRD, dried blood Phe/Tyr ratio exceeded 4.6 (plasma Phe/Tyr ratio >5.4) after 2 h and biopterin concentration in dried blood remained below 16.2 nmol/L (plasma biopterin <14 nmol/L) 1 h after Phe challenge.

CONCLUSIONS: Phe loading is a useful tool for diagnosing DRD in children. Test duration can be reduced to only 2 h, and specific pediatric cutoff values need to be applied. Simultaneous measurements of the Phe/Tyr ratio and biopterin in plasma or DBS are essential in pediatric patients.

OBJECTIVES: The objectives of this study were to determine the value of phenylalanine (Phe) loading for diagnosing dopa-responsive dystonia (DRD) in children.

METHODS: We investigated orally administered Phe loading tests (100 mg/kg) in seven patients with confirmed DRD and 17 pediatric patients with clinically suspected but excluded DRD. Results of Phe, tyrosine (Tyr), and biopterin from plasma and dried blood spot (DBS) analyses were correlated, and pediatric cutoff values established.

RESULTS: The peak Phe concentration following a Phe load in the pediatric DRD population is lower than reported in adults. By using adult cutoff values and either Phe/Try ratios or biopterin concentrations only, false positive and false negative results are frequent. Only the combined analysis of the Phe/Tyr ratio and biopterin concentration is reliable in children. In children with DRD, dried blood Phe/Tyr ratio exceeded 4.6 (plasma Phe/Tyr ratio >5.4) after 2 h and biopterin concentration in dried blood remained below 16.2 nmol/L (plasma biopterin <14 nmol/L) 1 h after Phe challenge.

CONCLUSIONS: Phe loading is a useful tool for diagnosing DRD in children. Test duration can be reduced to only 2 h, and specific pediatric cutoff values need to be applied. Simultaneous measurements of the Phe/Tyr ratio and biopterin in plasma or DBS are essential in pediatric patients.

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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
Language:English
Date:December 2010
Deposited On:14 Jan 2011 15:39
Last Modified:05 Apr 2016 14:34
Publisher:Springer
ISSN:0141-8955
Publisher DOI:10.1007/s10545-010-9164-9
PubMed ID:20668943
Permanent URL: http://doi.org/10.5167/uzh-42004

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