Tay-Sachs disease is a rare inherited disorder that results in the progressive destruction of nerve cells in the brain and spinal cord.
The disease affects boys and girls equally. In its most common form, the disease becomes evident between three and six months of age, when previously normal infants begin to slow in their development and gradually lose their ability to move (see Symptoms section, above).
Eventually, they become blind and die prematurely, usually before five years of age.
Other, even rarer forms of Tay-Sachs disease can arise in later childhood, adolescence and adulthood. The severity of these types vary, but are usually milder than the disease seen in infants.
There is currently no cure for Tay-Sachs disease, although a number of the symptoms can be effectively managed.
What is the cause?
Tay-Sachs disease is caused by the absence of a vital enzyme called Hexosaminidase-A (Hex-A) (see Causes section, above). Without this enzyme, a fatty substance called ganglioside builds up in the cells of the nervous system, causing them to stop working normally and eventually killing them.
The absence of this enzyme results from inheriting two copies of a faulty gene. Inheriting one copy from one parent will not cause disease. This is called autosomal recessive inheritance. It means that, in order for a child to develop the disease, the faulty gene must have been passed on from both parents (one copy from each).
How common is it?
The disease is very rare in the general population, affecting about one person in every 250,000 to 300,000.
However, the faulty gene is much more common in people of Ashkenazi (eastern and central European) Jewish descent. Tay-Sachs disease has tended to occur more often in this population, with one person in 30 carrying the faulty gene and about one in 3,600 infants developing the disease.
However, with improved community awareness and the availability of prenatal testing, the frequency of Tay-Sachs disease has greatly decreased and most new patients in the UK and Europe do not have Jewish ancestry.
