Abstract
In this group of conditions, GM2 ganglioside and related compounds accumulate in lysosomes due to enzymatic deficiencies in their degradation pathways. Their typical presentation is that of a pure neurodegenerative disorder characterized by developmental arrest, worsening neurological deficits and a shortened life span (Kolodny, 1966), although one of its variants, infantile Sandhoff’s disease, may manifest systemic involvement (see below). The extent and type of these manifestations, however, vary widely, ranging from a relatively acute presentation to a more slowly progressive syndrome characterized by either motor deficits-in the form of worsening extrapyramidal or motor neuron disease- or behavioral changes-such as psychiatric symptoms or dementia in young adulthood. This variation in the clinical picture seems to be associated with different degrees of residual enzyme activity, which lead to corresponding severities of their clinical manifestations (i.e., the most severe deficits showing the most aggressive and early phenotypes. This situation is very similar to that of GM1 gangliosidosis. The prototype of this group of conditions is Tay-Sachs disease.