Sandhoff disease is a lysosomal storage disorder with a wide range of symptoms that are virtually indistinguishable from those seen in patients with Tay-Sachs disease. Patients are usually classified as having infantile, juvenile or adult forms depending upon the age of onset. The infantile form is the most severe with onset by 6 months of age and death typically before 4 years. Infants generally appear normal at birth; at 3-6 months of age motor weakness, hypotonia and an exaggerated startle reaction are usually the presenting features followed by developmental retardation and regression, loss of vision and eventually blindness, spasticity, disordered swallowing and seizures. A “cherry-red” spot on the retina is a typical funduscopic finding. Macrocephaly appears by about 18 months, with death by the second or third year, often due to aspiration pneumonia. In Sandhoff disease organomegaly and bony abnormalities are rarely observed. The late infantile and juvenile forms present at about 2 to 10 years of age with ataxia, incoordination and dysarthria, followed by progressive psychomotor deterioration, spasticity and seizures. Cherry red spots may not be present. The chronic and adult forms may show variable presentations with pyramidal and extrapyramidal signs, movement disorders, psychosis, lower motor neuron and spinocerebellar dysfunction, autonomic dysfunction or spinocerebellar degeneration. Several geographically isolated populations have a high incidence of Sandhoff disease, including an inbred community of Metis Indians in northern Saskatchewan and individuals from the northwestern region of the province of C?rdoba and the central southern region of the province of La Roija in Argentina where the carrier frequency is estimated to be 1 in every 16-29 persons. In the general population, the incidence of Sandhoff disease is estimated at 1 in 300,000 births.