The<unk>  are a group of three related genetic disorders that result from a deficiency of the enzyme beta-hexosaminidase. This enzyme catalyzes the biodegradation of fatty acid derivatives known as gangliosides. The diseases are better known by their individual names: Tay–Sachs disease, AB variant, and Sandhoff disease. Beta-hexosaminidase is a vital hydrolytic enzyme, found in the lysosomes, that breaks down lipids. When beta-hexosaminidase is no longer functioning properly, the lipids accumulate in the nervous tissue of the brain and cause problems. Gangliosides are made and biodegraded rapidly in early life as the brain develops. Except in some rare, late-onset forms, the<unk>  are fatal. All three disorders are rare in the general population. Tay–Sachs disease has become famous as a public health model because an enzyme assay test for TSD was discovered and developed in the late 1960s and early 1970s, providing one of the first "mass screening" tools in medical genetics. It became a research and public health model for understanding and preventing all autosomal genetic disorders. Tay–Sachs disease, AB variant, and Sandhoff disease might easily have been defined together as a single disease, because the three disorders are associated with failure of the same metabolic pathway and have the same outcome. Classification and naming for many genetic disorders reflects history, because most diseases were first observed and classified based on biochemistry and pathophysiology before genetic diagnosis was available. However, the three<unk>  were discovered and named separately. Each represents a distinct molecular point of failure in a subunit that is required for activation of the enzyme.
GM2 gangliosidoses
GM1 gangliosidoses
Beta-mannosidosis
Sphingolipidoses
GM2-gangliosidosis, AB variant
Glycogen storage disease type 0
Congenital disorder of glycosylation type IIc
Galactosialidosis