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Hurler-like phenotype: enzymatic diagnosis in dried blood spots on filter paper
N A Chamoles1, M B Blanco, D Gaggioli
1Laboratory of Neurochemistry, Uriarte 2383, 1425 Buenos Aires, Argentina. nachamoles@fibertel.com.ar
Background:
Clinical differentiation among mucopolysaccharidosis, oligosaccharidosis, and mucolipidosis II and III is difficult. We describe methods for the assay of 8 lysosomal enzymes in dried blood spots on filter paper that allow screening for 12 lysosomal storage diseases that present with a Hurler-like phenotype.
Methods:
To test tubes containing 3-mm blood spots, we added elution liquid and fluorescent or radioactive substrate solution. After incubation at 37 degrees C, the reaction was terminated by the addition of a stop buffer. The amount of hydrolyzed product was compared with a calibrator to allow the quantification of enzyme activity. Sample stability was studied during storage for 21 days and during shipment of samples. We measured enzyme activities in 85 healthy controls (35 newborn, 50 adult), 57 patients suffering from 11 lysosomal storage diseases, and 46 obligate carriers.
Results:
Intra- and interassay CVs were <9% and <15%, respectively. Mean activity losses during transportation or storage for up to 21 days at 4 degrees C were < or =27%. Enzyme activities in all patients were outside the ranges of values seen for carriers and controls.
Conclusions:
The described methodology distinguishes between patients and controls with samples that are sufficiently stable to be mailed to the testing laboratory.