Tay–Sachs disease (also known as GM2 gangliosidosis or hexosaminidase A deficiency) is an autosomal recessive genetic disorder. In its most common variant (known as infantile Tay–Sachs disease), it causes a progressive deterioration of mental and physical abilities that commences around six months of age and usually results in death by the age of four. The disease occurs when harmful quantities of cell membrane components known as gangliosides accumulate in the brain's nerve cells, eventually leading to the premature death of the cells. Tay–Sachs disease is classified into several forms, which are differentiated based on the onset age of neurological symptoms. Infantile Tay–Sachs disease. Infants with Tay–Sachs disease appear to develop normally for the first six months after birth. Then, as neurons become distended with gangliosides, a relentless deterioration of mental and physical abilities begins. The child becomes blind, deaf, unable to swallow, atrophied, and paralytic. Death usually occurs before the age of four. Juvenile Tay–Sachs disease. Juvenile Tay–Sachs disease is rarer than other forms of Tay–Sachs, and usually is initially seen in children between two and ten years old. People with Tay–Sachs disease develop cognitive and motor skill deterioration, dysarthria, dysphagia, ataxia, and spasticity. Death usually occurs between the age of five to fifteen years. Adult/Late-Onset Tay–Sachs disease.