Immunological evidence for deficiency in an activator protein for sulfatide sulfatase in a variant form of metachromatic leukodystrophy.

Cultured skin fibroblasts from the patient described by Shapiro and co-workers as having a variant form of metachromatic leukodystrophy (MLD) [Shapiro, L.J., Aleck, K. A., Kaback, M.M., Itabashi, H., Desnick, R.J., Brand, N., Stephens, R.L., Fluharty, A.L. & Kihara, H. (1979) Pediatr. Res. 13, 1179-1181] were confirmed to have a partial deficiency (25-40% of controls) of arylsulfatase A activity in vitro and a severe inability to metabolize [14C]stearic acid-labeled sulfatide presented in the medium. When 150 micrograms of purified activator protein for GM1 ganglioside beta-galactosidase and sulfatide sulfatase was added in 4 ml of medium with the 14C-labeled sulfatide, correction of the sulfatide metabolism to the normal range was found. Monospecific antibodies to this activator protein were prepared in rabbits, and they were used to examine cultured cells for the presence of crossreacting material by Ouchterlony double immunodiffusion and rocket immunoelectrophoresis. Cell extracts from controls and from patients with GM1 gangliosidosis and MLD were found to have a single line of identity. By comparison to known concentrations of purified activator protein, cell extracts from controls were found to have 0.76 +/- 0.32 micrograms of activator protein (mean +/- 1 SD, n = 10) per mg of solubilized protein, whereas those from patients with type 1 GM1 gangliosidosis and late infantile MLD had 1.53 and 1.41 micrograms/mg, respectively. Cell extracts from the patient with a variant form of MLD had no visible precipitin line by Ouchterlony double immunodiffusion and only a diffuse nonspecific region of staining by rocket immunoelectrophoresis. These immunologic studies provide evidence for a deficiency in the activator protein required for normal catabolism of sulfatide in the cells from this patient and possibly provide a method for diagnosis of similar patients.