Many of the known gene defects result in inborn errors of metabolism that produce irreversible damage to the central nervous system. A variety of new clinical, morphologic, biochemical, and genetic techniques are being used to characterize these disorders more precisely. At the Shriver Center, the different genotypes of GM2-gangliosidosis are distinguished according to the ability of cells in culture to metabolize radioactively-labeled GM2-ganglioside. Large-scale screening for carriers of the trait for Tay-Sachs disease, the most common of the GM2-gangliosidoses, has dramatically reduced the incidence of this disease. Current efforts to isolate the genes for the alpha and beta chains of hexosaminidase A will lay the groundwork for better understanding of the molecular defects in these diseases and offers hope for a possible treatment.