Tay-Sachs disease is a rare genetic disorder characterized by progressive degeneration of nerve cells in the brain and spinal cord. The signs and symptoms vary depending on the age of onset and type of disease. There are three main forms of Tay-Sachs disease: acute infantile, juvenile and adult-onset. 1. Acute infantile form This is the most commonly observed form. The age of onset is 3-6 months, and gradually affects motor and intellectual development. Typical symptoms include loss of motor skills, over-reactive response to loud noises, seizures, vision problems and hearing problems. Affected children do not normally survive past the age of 4. 2. Juvenile form This form is rare. The age of onset is between 2 to 10 years of age. The signs and symptoms are similar to the infantile form, but typically milder. 3. Adult-onset form This form is also rare. The age of onset ranges from adolescence to mid thirties. The rate of neurodegeneration for this form is slower, and the symptoms can be quite variable between affected individuals. Tay-Sachs disease is caused by mutations in the HEXA gene, which encodes beta-hexosaminidase A. This enzyme helps to break down a fatty substance called GM2 ganglioside in the lysosome for recycling. Mutations in the HEXA gene prevent or reduce the enzymatic activity of beta-hexosaminidase A. Without functional beta-hexosaminidase A, GM2 ganglioside cannot be broken down properly, resulting in a toxic accumulation of fatty substances in cells, particularly the nerve cells in the brain and spinal cord. Excessive levels of GM2 ganglioside lead to neuronal destruction, resulting in the characteristic features of Tay-Sachs disease. References: Jose CP, Ferreira MD, Schreiber-Agus N, Carter SM, Klugman S, MDa, Gregg AR, Gross SJ (2014). Carrier testing for Ashkenazi Jewish disorders in the prenatal setting: navigating the genetic maze. American Journal of Obstetrics and Gynecology. 211(3): 197-204. Kaback MM, Desnick RJ (1999)