INCREASED GLOBOTRIAOSYLCERAMIDE ON PLASMA-MEMBRANES OF SYNCHRONIZED FAMILIAL DYSAUTONOMIA CELLS - VEROTOXIN BINDING-STUDIES

Familial dysautonomia is an autosomal recessive genetic disease found almost exclusively among Ashkenazi Jews, characterized by deficits in autonomic, sensory, and central functions. Although the gene has been localized to chromosome 9, the biochemical defect remains elusive. We previously reported an increase in globotriaosylceramide in dysautonom ic fibroblasts and lymphoblasts, and unusual fibroblast growth pattern s suggesting plasma membrane abnormalities. Globotriaosylceramide is a plasma membrane component, and the natural receptor for verotoxin der ived from E. coil. In Vero and HeLa cells, which are susceptible to ve rotoxin, the expression of globotriaosylceramide on the cell surface i s maximal at the G1/S boundary of the cell cycle. Measurement of toxin binding at 0 degrees C at this boundary is indicative of the amount o f globotriaosylceramide exposed on the cell surface. Above 0 degrees C , verotoxin enters, and is toxic to, the cell. We analyzed verotoxin-g lobotriaosylceramide interactions in synchronized FD and normal cells at this boundary. I-125-toxin binding was much more marked to lymphobl asts from patients than from controls. When cells were grown in the pr esence of verotoxin, at 10(-2)-10(-7) mu g/mL, 70% of dysautonomic lym phoblasts died, compared to 25% of controls. The CD50 was 10 ng/mL for dysautonomic fibroblasts vs 450 for controls. These results may be ex ploited to create a biological assay to differentiate between FD and n ormal cells.