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Tay-Sachs Disease (TSD)
Thursday, 04 August 2005
Sunday, 28 August 2005

What

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. 

Who

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.

Signs and Symptoms

There are various forms of TSD, and the signs and symptoms of the disorder differ depending on age:

  1. Infantile (classic) form: Infants affected with the classic acute infantile form of the disease are usually completely normal at birth.  By 3-6 months of age, they develop a mild weakness and an exaggerated startle response. Within a few months, the child may stop attaining new skills and may lose some of the abilities and skills they had previously attained. Infants may have decreased visual attention and unusual eyes movements.  The progression of the disease is rapid and by 1 year, seizures become common.  There is decreased purposeful movement and visual loss.  By 2 years of age the child becomes progressively less responsive with worsening seizures and problems with swallowing.  Death, often from pneumonia, usually occurs between 2-4 years of age.
  2. Juvenile form: The juvenile form usually appears between 2 and 10 years with clumsiness and trouble walking.  This is often followed by recurrent seizures and diminishing mental function. Development regresses with increasing loss of muscle strength, and  the development of spasticity. Eventually, the child becomes blind, rigid and unresponsive.  Death usually occurs between 10-15 years of age.
  3. Chronic form and adult onset: These latter forms are characterized by a variety of neurological findings including uncontrollable movements, clumsiness and trouble walking, and difficulty speaking. The adult onset form may be accompanied by psychiatric manifestations and may resemble ALS (Lou Gehrig's disease).

Possible Causes

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.

Diagnosis

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.

Treatment

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.

Prognosis

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.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

National Tay Sachs and Allied Disorders Association

http://www.ntsad.org/

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.

Medline Plus

http://www.nlm.nih.gov/medlineplus/taysachsdisease.html

A well written article on Tay Sachs with nice definitions of technical terms.

Mazornet-Jewish Genetic Disease

http://www.mazornet.com/genetics/tay-sachs.asp

A nice website with information about the disease as well as available support.

REFERENCES AND SOURCES:  

National Human Genome Research Institute

www/gemp,e/gov/page.cfm?pageID=10001220

www.intelihealth.com/IH/ihtIH/WSIHW000/9339/11032.html

McCance, K (2002). Pathophysiology: the biologic basis for disease in adults and children, 4th Edition, Mosby, p. 578-9

Google Search for Tay-Sachs Disease (TSD)

References and Sources

National Human Genome Research Institute www/gemp,e/gov/page.cfm?pageID=10001220 www.intelihealth.com/IH/ihtIH/WSIHW000/9339/11032.html McCance, K (2002). Pathophysiology: the biologic basis for disease in adults and children, 4th Edition, Mosby, p. 578-9