Abstract
Mucopolysaccharidosis type IVA or Morquio type-A disease is a hereditary lysosomal storage disorder caused by deficient activity of the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS). The disease is caused by lysosomal accumulation of unprocessed glycosaminoglycans (GAGs) that manifests with severe to mild skeletal and cardiopulmonary abnormalities. We have developed a modified microtiter plate-based enzyme activity assay using dried blood spots and a fluorescent substrate for measuring specific GALNS activity to identify patients with MPS IVA.