Metabolic defect: beta-hexosaminidase (alpha chain) deficiency Other sphingolipid degradation diseases: acid sphingomyelinase deficiency | Fabry | Farber | Gaucher: type I, type II, type III | GM1 gangliosidosis: type I, type II, type III | Tay-Sachs: type I, type II | Sandhoff: type I | Krabbé | metachromatic leukodystrophy: type I, type II, type III

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Results from a defect in the alpha chain of beta-hexosaminidase. Beta-hexosaminidase A isoenzyme contains an alpha and a beta chain (beta-hexosaminidase B isoenzyme contains two beta chains); Tay-Sachs affects only the A isoenzyme. (By comparison, Sandhoff disease, which results from a beta-chain defect, affects both isoenzymes.) Enzyme deficiency results in accumulation of GM2 gangliosides in the central nervous system. The infantile form has a complete deficiency of beta-hexosaminidase activity (other forms have a partial deficiency).

Motor/muscle weakness		Motor/muscle weakness		Motor/muscle weakness

Adult form involves a wide range of neurologic symptoms and abnormal findings, with symptoms of spinocerebellar and lower motor neuron dysfunction most prominent. Tends to show progressive muscle weakness, dysarthia, psychiatric manifestations (without dementia), and fasciculations.

Spinocerebellar and lower motor neuron dysfunction:

Motor weakness

Tremor

Personality changes

Psychoses

Depression

Normal intelligence

1. Hauser SL, Longo DL, eds. Harrison’s Principles of Internal Medicine. 14th ed. New York: McGraw-Hill; 1998; p. 2171.

2. Kaback, Michael M, MD. “Hexosaminidase A Deficiency.” www.genetests.org. Updated 9 January 2004.

3. University of Pittsburgh, Lysosomal Disease Center. www.pitt.edu/AFShome/g/e/geneorb/public/html/courses/lyso_trials/gm2.html Accessed July 2004.

4. Meikle PJ, Hopwood JJ, Clague AE, Carey WF. Prevalence of Lysosomal Storage Disorders. JAMA. 1999; 281: 249-254.