Tay-Sachs disease is a rare, inherited neurodegenerative disease. People with Tay-Sachs disease do not have enough of an enzyme called beta-hexosaminidase A. The less enzyme a person has, the more severe the disease and the earlier that symptoms appear. Infantile - the most common severe form, with symptoms appearing in the first few months of life. Symptoms include a loss of skills learned (regression), seizures, and loss of muscle and mental functions. Symptoms include behavior problems, gradual loss of skills, frequent respiratory infections, and seizures. Symptoms may include clumsiness, muscle weakness, psychiatric disorders, and gradual loss of skills, often leading to the need for mobility assistance. Intellect and behavior become impaired in some cases. The lifespan varies from shortened to unaffected. Tay-Sachs disease is caused by genetic changes in the HEXA gene and inheritance is autosomal recessive. The HEXA gene gives the body instructions to make part of the beta-hexosaminidase A enzyme, which is needed to break down a substance called GM2 ganglioside. When the enzyme is not functional or not made, GM2 ganglioside builds up in the nerve cells (neurons) of the brain and spinal cord, causing the symptoms of the disease. The diagnosis of Tay-Sachs disease involves a blood test that detects absent or very low levels of beta-hexosaminidase A enzyme activity. Molecular genetic testing of the HEXA gene may be used to identify the specific genetic changes present, or to rule out the disease if a false-positive blood test result is suspected.