Diagnosis of feline GM1 gangliosidosis by enzyme assay of cultured conjunctival cells.

GM1 gangliosidosis is characterized by a deficiency in the lysosomal hydrolase beta-galactosidase, progressive nervous system disease and ocular lesions. Diagnosis of GM1 gangliosidosis in humans and cats with the analogous disease has been made by measurement of the enzyme activity in various tissues including brain, liver and cultured skin fibroblasts. The authors report the use of cultured conjunctival cells for this purpose derived from cats with feline GM1 gangliosidosis, a model of the human disease (juvenile GM1 gangliosidosis, Derry's disease). Full thickness conjunctival biopsies from three cats with GM1 gangliosidosis and two normal controls were used to initiate cell cultures. Optimal conditions for beta-galactosidase activity were established with an uncultured conjunctival biopsy from a normal cat. The fluorgen, 4-methylumbelliferyl-beta-D-galactopyranoside was used as substrate. After 2 months in culture, and 2 weeks after subculture, cells from cats affected with GM1 gangliosidosis exhibited specific activities for beta-galactosidase of 10, 9 and 12 nmoles 4MU/hr/mg protein, whereas specific activities for normals were 630 and 469 nmoles 4MU/hr/mg. Enzymatic analysis of cultured conjunctival cells may offer an effective alternative for the diagnosis of GM1 gangliosidosis.