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Tay-Sachs disease (TSD) is a progressive neurologic disorder, most commonly occurring in children, that results in destruction of the nervous system. It is an autosomal recessive disease, meaning that affected individuals must inherit one defective gene from each parent. This disorder is categorized as a lysosomal storage disease. Lysosomes are the major digestive units in cells that contain enzymes to break down or "digest" nutrients, including certain complex carbohydrates and fats.
The incidence of Tay-Sachs disease is significantly higher among people of eastern European (Ashkenazi) Jewish descent. The carrier rate in the Ashkenazi Jewish population is approximately 1 in 30, and the disease incidence is 1 in 3600. Non-Jewish French Canadians also have a higher incidence of the disease. Also, children can be born to populations not thought to be at high risk, and the incidence in the general population is 1 in 360,000.
There are various forms of TSD, and the signs and symptoms of the disorder differ depending on age:
Tay-Sachs is caused by the absence of a vital enzyme called hexosaminidase-A (Hex-A). Without the Hex-A enzyme, a fatty substance or lipid called GM2 ganglioside accumulates abnormally in cells, especially in the nerve cells (neurons) of the brain. This accumulation causes progressive damage to the cells. In children, the destructive process begins in the fetus early in pregnancy, although the disease is not clinically apparent until the child is several months old. By the time a child with Tay-Sachs is 3 to 4 years old, the nervous system is affected to the degree that death usually occurs by age 5.
Tay-Sachs disease can be diagnosed before birth through amniocentesis (sampling of fluid surrounding the fetus) or chorionic villus sampling (CVS), a sampling of maternal tissue. Both samples can be sent for genetic analysis. Screening by blood sampling is recommended for all couples of Ashkenazi (eastern European) Jewish ancestry and for others with a family history of the disease. After birth, diagnosis is based on the above mentioned clinical features of TSD along with blood tests showing deficient Hex A enzyme activity.
Although there is no cure for Tay-Sachs disease, researchers are actively pursuing several possible treatments such as enzyme replacement, bone marrow transplantation, and gene therapy. Currently treatment is aimed at relieving symptoms and making the child and family comfortable. For example, tube feedings provide nutritional supplements to maintain growth and weight, suctioning and drainage maintain an open airway to promote proper breathing and resist infections, skin care prevents pressure ulcers in bedridden children and laxatives help relieve constipation.
The classic infantile form of Tay-Sachs disease is uniformly fatal with progressive mental and motor deterioration which leads to death before the age of 5 years. The other forms have better prognosis although the ultimate life spans are not known, as they are dependent on the complications and progression of symptoms. In general, the earlier the child is afflicted, the more guarded the prognosis.
National Tay Sachs and Allied Disorders Association
A great site dedicated to providing information and support services to families affected by this disease. There are also links to websites with information about ongoing clinical trials.
A well written article on Tay Sachs with nice definitions of technical terms.
Mazornet-Jewish Genetic Disease
A nice website with information about the disease as well as available support.
REFERENCES AND SOURCES:
National Human Genome Research Institute
McCance, K (2002). Pathophysiology: the biologic basis for disease in adults and children, 4th Edition, Mosby, p. 578-9