Sphingolipidoses are caused by genetic defects in a series of lysosomal enzymes and other proteins essential for the catabolism of sphingolipids. These enzymes are involved in degradation of lipids that contain sphingosine as the basic building block (Fig. 41-1, Table 41-2) (Chap. 3). Since the nervous system is rich in these lipids, many disorders in this category manifest as neurological disorders. Sphingolipids are degraded by sequential removal of the terminal moieties of the hydrophilic chain: sulfate in the case of sulfatide, phosphorylcholine in the case of sphingomyelin and sialic acid or sugar moieties in others, to ceramide and then to sphingosine and fatty acid. Genetic disorders are known in humans affecting almost every step of the degradative pathway. The mode of inheritance is Mendelian autosomal recessive for all sphingolipidoses, except for Fabry's disease, which is an X-linked disorder (Fig. 41-1, Table 41-2).