Abstract
Interest in newborn screening for mucopolysaccharidoses (MPS) is growing, due in part to ongoing efforts to develop new therapies for these disorders and new screening assays to identify increased risk for the individual MPSs on the basis of deficiency in the cognate enzyme. Existing tests for MPSs utilize either fluorescence or mass spectrometry detection methods to measure biomarkers of disease (e.g., enzyme function or glycosaminoglycans) using either urine or dried blood spot (DBS) samples. There are currently two approaches to fluorescence-based enzyme function assays from DBS: (1) manual reaction mixing, incubation, and termination followed by detection on a microtiter plate reader; and (2) miniaturized automation of these same assay steps using digital microfluidics technology. This article describes the origins of laboratory assays for enzyme activity measurement, the maturation and clinical application of fluorescent enzyme assays for MPS newborn screening, and considerations for future expansion of the technology.
Highlights
Mucopolysaccharidoses (MPS) are a collection of at least 11 rare genetic disorders that are progressive and vary widely in severity
Minami et al compared the activities of two different substrates—a colorimetric phenyl-α-l-iduronide to a fluorescent 4-methylumbelliferyl derivatives (4-MU)-α-l-iduronide using leukocytes and lymphoblastoid cells obtained from patients with MPS I Hurler and Scheie syndromes [32]
We recently demonstrated a multiplexed fluorescence assay for α-galactosidase (GLA) and GLB1 within the same droplet, in which the substrates were conjugated to 4-MU and resorufin dyes, respectively
Summary
Mucopolysaccharidoses (MPS) are a collection of at least 11 rare genetic disorders that are progressive and vary widely in severity. Tomatsu et al estimate that as many as 200 babies are born each year in the United States that are affected with one type of MPS [2]. Rare, these disorders are devastating to children and their families [3]. Scissors indicate the sites cleaved in each of the glycosaminoglycans (GAGs) by the various enzymes. GUSB cleaves dermatan sulfate after GlcA residues are exposed by other enzymes. Gal: GUSB cleaves dermatan sulfate after GlcA residues are exposed by other enzymes. Specific enzyme deficiency, but usually include facial dysmorphism, hepatosplenomegaly, cardiac, Elevated. GAG abbreviations: dermatan sulfate (DS), heparan sulfate (HS), keratan sulfate (KS), chondroitin sulfate (CS)
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