Partial deficiency of glycoprotein neuraminidase in some patients with Morquio disease type A

A deficiency of glycoprotein neuraminidase (sialidase, acylneuraminyl hydrolase, EC 3.2.1.18) activity was found in fibroblasts from a patient with the clinical symptoms of Morquio disease type A (mucopolysaccharidosis IV A). Residual neuraminidase activity was about 5% of the mean normal activity. N-Acetylgalactosamine-6-sulfate (GalNAc-6-S) sulfatase activity was reduced to less than 1% of normal with a pH-optimum of 3.0 as expected for the severe form of Morquio disease. In peripheral leucocytes of the patient, however, neuraminidase activity but not Ga1NAc-6-S sulfatase activity was in the normal range. Mixing experiments excluded the presence of excessive amounts of inhibitors of neuraminidase activity.