Optimization of enzymatic diagnosis for mucopolysaccharidosis I in dried blood spots on filter paper

• We propose an ultramicroassay for the diagnosis of MPS I in dried blood spots.
• Hemoglobin's interference was decreased, optimizing enzymatic diagnosis for MPS I.
• Enzyme activity's underestimation reported by using other assays was eliminated.
• Discrimination between healthy individuals and patients increased vs. other assays.
• This assay has the potential to be used in neonatal screening programs for MPS I.

ObjectivesThe aim of this study was to validate an ultramicroassay with a reduced interference of hemoglobin for the enzymatic diagnosis of mucopolysaccharidosis I in dried blood spots on filter paper.Design and methodsA matrix of dried blood was incorporated within the calibration system. In addition, trichloroacetic acid was added to precipitate hemoglobin. Linearity, precision, accuracy and limits of detection and quantification were determined and α-l-iduronidase activity was obtained from 6 patients, 9 heterozygotes, 25 healthy adults and 500 neonates.ResultsThe ultramicroassay was linear, precise (coefficients of variation less than 10%) and accurate (recovery between 91 and 98%). The interference of hemoglobin was decreased within the hematocrit range of clinical interest: 35–55%.ConclusionsThis ultramicroassay increases in 2.5 times the difference between healthy individuals and patients with respect to the reference assay; optimizing enzymatic quantification and confirmatory biochemical diagnosis for mucopolysaccharidosis I.

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