Tandem Mass Spectrometry for the Direct Assay of Lysosomal Enzymes in Dried Blood Spots: Application to Screening Newborns for Mucopolysaccharidosis I

Treatments now available for mucopolysaccharidosis I require early detection for optimum therapy. Therefore, we have developed an assay appropriate for newborn screening of the activity of the relevant enzyme, alpha-L-iduronidase. We synthesized a new alpha-L-iduronidase substrate that can be used t...

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Bibliographic Details
Published in:Clinical chemistry (Baltimore, Md.) Md.), 2008-12, Vol.54 (12), p.2067-2070
Main Authors: Blanchard, Sophie, Sadilek, Martin, Scott, C. Ronald, Turecek, Frantisek, Gelb, Michael H
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Babies
Biological and medical sciences
Blood
Carbon dioxide
Congenital diseases
Enzymes
Fluorometry
Fundamental and applied biological sciences. Psychology
Heparan sulfate
Humans
Iduronidase - blood
Immunoassay
Infant, Newborn
Investigative techniques, diagnostic techniques (general aspects)
Lysosomes - enzymology
Mass spectrometry
Medical sciences
Molecular weight
Mucopolysaccharidosis I - epidemiology
Neonatal Screening - methods
Tandem Mass Spectrometry
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Summary:Treatments now available for mucopolysaccharidosis I require early detection for optimum therapy. Therefore, we have developed an assay appropriate for newborn screening of the activity of the relevant enzyme, alpha-L-iduronidase. We synthesized a new alpha-L-iduronidase substrate that can be used to assay the enzyme by use of tandem mass spectrometry together with an internal standard or by fluorometry. The assay uses a dried blood spot on a newborn screening card as the enzyme source. The assay protocol uses a simple liquid-liquid extraction step before mass spectrometry. We optimized enzyme reaction conditions and procedures for the assay, including the concentration of substrate, the reaction pH, the incubation time, and mass spectrometer operation. We also assessed inter- and intraassay imprecision. When the assay was tested on dried blood spots, the alpha-L-iduronidase activity measured for 5 patients with mucopolysaccharidosis I was well below the interval found for 10 randomly chosen newborns. Inter- and intraassay imprecision were
ISSN:0009-9147
1530-8561
DOI:10.1373/clinchem.2008.115410