Sialidosis: delineation of subtypes by neuraminidase assay.

A sensitive assay for acid neuraminidase using 4–methylumbelliferyl-α-D-N-acetylneura-mink acid is described. In skin fibroblasts, patients with sialidosis Types 1 and 2 have severe deficiencies of neuraminidase activity compared with controls. Patients with Type 1 sialidosis have activities which are 10 times higher than those with Type 2 sialidosis, in keeping with their milder clinical involvement. Two Italian patients with Type I sialidosis had a Km which was one-sixth normal; the other patients had a Km in the normal range.