From OMIM
Sandhoff disease is a progressive neurodegenerative disorder characterized by an accumulation of GM2 gangliosides, particularly in neurons, and is clinically indistinguishable from Tay-Sachs disease (272800).  http://www.omim.org/entry/268800

From MedlinePlus Genetics
Sandhoff disease is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spinal cord (central nervous system). This condition is classified into three major types based on the age at which signs and symptoms first appear: infantile, juvenile, and adult.

The infantile form of Sandhoff disease is the most common and severe form and becomes apparent in infancy. Infants with this disorder typically appear normal until the age of 3 to 6 months, when their development slows and muscles used for movement weaken. Affected infants lose motor skills such as turning over, sitting, and crawling. They also develop an exaggerated startle reaction to loud noises. As the disease progresses, children with Sandhoff disease experience seizures, vision and hearing loss, and intellectual disability. An eye abnormality called a cherry-red spot, which can be identified with an eye examination, is characteristic of this disorder. Some affected children also have distinctive facial features, enlarged organs (organomegaly), or bone abnormalities. Children with the infantile form of Sandhoff disease usually live only into early childhood.

The juvenile and adult forms of Sandhoff disease are very rare. Signs and symptoms are usually milder than those seen with the infantile form, although they vary widely. The juvenile form can begin between ages 2 and 10.  Characteristic features include speech difficulties, loss of cognitive function (dementia), seizures, and  loss of muscle coordination (ataxia). Adult Sandhoff disease is characterized by problems with movement and psychiatric problems.  https://medlineplus.gov/genetics/condition/sandhoff-disease