Tay-Sachs – a fatal genetic disorder


Kolkata, Jul 7 : Tay-Sachs disease is a fatal genetic disorder in which harmful quantities of a fatty substance called Ganglioside GM2 accumulate in the nerve cells in the brain.
According to World Health Organization (WHO), this is caused by a decrease in the functioning of the Hexosaminidase A enzyme. Abnormal Hexosaminidase A enzyme activity causes an accumulation of fat in nerve cells, leading to paralysis, dementia, blindness, psychoses, and even death.
Though the degradation of the central nervous system begins at the fetal stage, observations such as loss of peripheral vision and motor co-ordination are not seen until about 6 months of age. This disease is autosomal recessive which means that an individual must inherit two defective genes, one from each parent, to inherit this disease.
According to the age of onset there are two existing forms of Tay-Sachs disease.–Infantile Tay-Sachs disease and Late onset Tay-Sachs disease ( chronic GM2-gangliosidosis)
The frequency of the condition is much higher in Ashkenazi Jews of Eastern European origin than in others.
Approximately one in every 27 Jews in the United States of America is a carrier of the TSD gene. There is also a noticeable incidence of TSD in non-Jewish French Canadians living near the St. Lawrence River and in the Cajun community of Louisiana. By contrast, the carrier rate in the general population as well as in Jews of Sephardic origin is about one in 250.
Among Jews of Sephardic origin and in the general, non-Jewish population, the carrier rate is about 1 in 250. There are certain exceptions. French-Canadian and the Cajun community of Louisiana have the same carrier rate as Ashkenazi Jews, one in 27.
Also, individuals with ancestry from Ireland are at increased risk for the Tay-Sachs gene. Current research indicates that among Irish Americans, the carrier rate is about one in 50.
The diagnosis for Tay- Sachs disease (TSD) can be made via a blood test in which the Hex A enzyme can be measured in either the serum, the white blood cells, or in the skin fibroblast.
Over the past 25 years, carrier screening and genetic counselling within high-risk populations have greatly reduced the number of children born with TSD in these groups. Therefore, a great percentage of the babies born with Tay-Sachs Disease today are born to couples who were not previously thought to be at significant risk.
Prenatal tests that can diagnose Tay-Sachs in the fetus before birth are available. These procedures are referred to as Amniocentesis and Chorionic Villus Sampling. Amniocentesis sampling is performed between the 15th and 16th week of pregnancy.
The procedure involves inserting a needle into the mother’s abdomen and obtaining a sample of the fluid that surrounds the baby. In Chorionic Villus Sampling a sample of cells from the placenta is retrieved by the doctor during the 10th and 12th week of pregnancy, and tested for the presence of Hex A.