Tandem mass spectrometry for the direct assay of enzymes in dried blood spots: application to newborn screening for mucopolysaccharidosis II (Hunter disease)

Background: A treatment for mucopolysaccharidosis II (Hunter syndrome) has recently become available. Therefore, we developed a high-throughput assay method appropriate for newborn screening for the relevant enzyme, iduronate 2-sulfatase. Methods: We synthesized a new iduronate 2-sulfatase substrate that can be used to assay the enzyme by use of tandem mass spectrometry together with an internal standard. The assay uses a dried blood spot on a newborn screening card as the enzyme source. Results: When the assay was tested on dried blood spots, the iduronate 2-sulfatase activity measured for 13 patients with Hunter syndrome was well below the interval found for 57 randomly chosen newborns. The assay was more sensitive than previously reported iduronate 2-sulfatase assays. Conclusions: This newly developed tandem mass spectrometry assay has the potential to be adopted for newborn screening of Hunter syndrome. This method also has the potential to be carried out in multiplex fashion to assay several different enzymes relevant to lysosomal storage diseases that are assayed in a single infusion into the mass spectrometer.