Received on October 10, 2005
Accepted on February 2, 2006

Molecular Diagnostics and Genetics

Detection of Mucopolysaccharidosis Type II by Measurement of Iduronate-2-Sulfatase in Dried Blood Spots and Plasma Samples

¹ Lysosomal Diseases Research Unit, Department of Genetic Medicine, Children, Youth and Women's Health Service, North Adelaide, South Australia, Australia
² Lysosomal Diseases Research Unit, Department of Genetic Medicine, Children, Youth and Women's Health Service, North Adelaide, South Australia, Australia, and Department of Paediatrics, University of Adelaide, South Australia, Australia

^* To whom correspondence should be addressed. E-mail: peter.meikle{at}adelaide.edu.au.

Background: Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder related to a deficiency in the enzyme iduronate-2-sulfatase (IDS). Clinical trials of enzyme replacement therapy are in progress, but effective treatment will require screening assays to enable early detection and diagnosis of MPS II. Our study evaluated the diagnostic accuracy of IDS protein and enzyme activity measurements in dried blood spots and plasma.

Methods: We collected dried-blood-spot and plasma samples from unaffected control individuals and from MPS II patients. We measured IDS protein concentration with a 2-step time-delayed dissociation-enhanced lanthanide fluorescence immunoassay. To measure enzyme activity, we immobilized anti-IDS antibody on microtiter plates to capture the enzyme and measured its activity with the fluorogenic substrate 4-methylumbelliferyl sulfate.

Results: Dried-blood-spot samples from MPS II patients showed an almost total absence of IDS activity (0-0.075 µmol · h^-1 · L^-1) compared with control blood spots (0.5-4.7 µmol · h^-1 · L^-1) and control plasma (0.17-8.1 µmol · h^-1 · L^-1). A dried-blood-spot sample from only 1 of 12 MPS II patients had detectable concentrations of IDS protein (24.8 µg/L), but no IDS protein was detected in plasma from MPS II patients. Ranges for IDS protein in control samples were 25.8-153 µg/L for blood spots and 22.8-349.4 µg/L for plasma.

Conclusion: Measurement of the IDS protein concentration and enzyme activity (as measured by a simple fluorogenic assay with an immune capture technique) enables identification of the majority of MPS II patient samples from both dried blood spots and plasma samples.