From OMIM
Tay-Sachs disease is an autosomal recessive, progressive neurodegenerative disorder which, in the classic infantile form, is usually fatal by age 2 or 3 years.  http://www.omim.org/entry/272800

From MedlinePlus Genetics
Tay-Sachs disease is a rare, inherited disorder that is characterized by neurological problems caused by  the death of nerve cells (neurons) in the brain and spinal cord (central nervous system).

The most common form of Tay-Sachs disease, known as infantile Tay-Sachs disease, becomes apparent early in life. Infants with this disorder typically develop normally until they are 3 to 6 months old. During this time, their development slows and muscles used for movement weaken. Affected infants stop achieving normal developmental milestones and begin to lose previously acquired skills such as turning over, sitting, and crawling. Infants with this condition develop an exaggerated startle reaction to loud noises. As the disease progresses, children with Tay-Sachs disease experience involuntary muscle twitches(myoclonic jerks), seizures, difficulty swallowing (dysphagia),vision and hearing loss, and intellectual disability. An eye abnormality called a cherry-red spot, which is identified by eye examination, is characteristic of this disorder. Children with infantile  Tay-Sachs disease usually live only into early childhood.

Two other forms of Tay-Sachs disease, known as juvenile and late-onset, are rare. Signs and symptoms of the juvenile form can appear between the ages of 5 years and late adolescence. Features of late-onset Tay-Sachs disease typically appear in adulthood. People with either of these forms of the condition usually have milder and more variable signs and symptoms than those with the infantile form. Characteristic features of juvenile or late-onset Tay-Saches disease include muscle weakness, loss of muscle coordination (ataxia), speech problems, and psychiatric symptoms. These signs and symptoms vary widely among people with late-onset forms of Tay-Sachs disease.  https://medlineplus.gov/genetics/condition/tay-sachs-disease