Sandhoff Disease

Clinical Characteristics
Ocular Features: 

Retinal ganglion cells are rendered dysfunctional from the toxic accumulation of intra-lysosomal GM2 ganglioside molecules causing early visual symptoms.  These cells in high density around the fovea centralis create a grayish-white appearance.  Since ganglion cells are absent in the foveolar region, this area retains the normal reddish appearance, producing the cherry-red spot.  Axonal decay and loss of the ganglion cells leads to optic atrophy and blindness. 

Systemic Features: 

Sandhoff disease may be clinically indistinguishable from Tay-Sachs disease even though the same enzyme is defective (albeit in separate subunits A and B that together comprise the functional enzymes).  The presence of hepatosplenomegaly in Sandoff disease may be distinguishing. The infantile form of this lysosomal storage disease seems to be the most severe.  Infants appear to be normal until about 3-6 months of age when neurological development slows and muscles become weak.  Seizures, loss of interest, and progressive paralysis begin after this together with loss of vision and hearing.  An exaggerated startle response is considered an early and helpful sign in the diagnosis.  Among infants with early onset disease, death usually occurs by 3 or 4 years of age.   

Ataxia with spinocerebellar degeneration, motor neuron disease, dementia, and progressive dystonia are more common in individuals with later onset of neurodegeneration.  The juvenile and adult-onset forms of the disease also progress more slowly.  

Genetics

Sandhoff disease results from mutations in the beta subunit of the hexosaminidase A and B enzymes.  It is an autosomal recessive disorder caused by mutations in HEXB (5q13). 

Tay-Sachs disease (272800) can be clinically indistinguishable from Sandoff disease and they are allelic disorders.  However, the mutation in Tay-Sachs (272800) is in HEXA resulting in dysfunction of the alpha subunit of hexosaminidase A enzyme. 

Treatment
Treatment Options: 

No specific treatment is available beyond general support with proper nutrition and maintainence of airways.  Anticonvulsants may be helpful in some stages.  Gene therapy in fibroblast cultures has achieved some restoration of  hexosaminidase A activity in Tay-Sachs disease and may have potential in Sandhoff disease as well. 

References
Article Title: 

References

Myerowitz R, Lawson D, Mizukami H, Mi Y, Tifft CJ, Proia RL. Molecular pathophysiology in Tay-Sachs and Sandhoff diseases as revealed by gene expression profiling. Hum Mol Genet. 2002 May 15;11(11):1343-50.

PubMedID: 12019216

Neufeld EF. Natural history and inherited disorders of a lysosomal enzyme, beta-hexosaminidase. J Biol Chem. 1989 Jul 5;264(19):10927-30. Review.

PubMedID: 2525553

Gilbert F, Kucherlapati R, Creagan RP, Murnane MJ, Darlington GJ, Ruddle FH. Tay-Sachs' and Sandhoff's diseases: the assignment of genes for hexosaminidase A and B to individual human chromosomes. Proc Natl Acad Sci U S A. 1975 Jan;72(1):263-7.

PubMedID: 1054503