In 2006 ExSAR applied for orphan drug designation from the FDA for Pyrimethamine (Pyrimethamine) for the treatment of patients affected with late-onset GM2-gangliosidosis. The application is pending the positive outcome of clinical trials. Pyrimethamine is an FDA-approved drug which readily passes the bloodbrain barrier (BBB). It is currently used to treat malaria and toxoplasmosis. Our in vitro cell-based studies with fibroblasts from these patients show that Pyrimethamine can function as a PC for Hex A and raise intracellular Hex A levels. Our hypothesis is that Pyrimethamine administered to adult TSD and SD patients can improve neurological function and health.