Tay-Sachs Disease - Topic Overview

Topic Overview

What is Tay-Sachs disease?

Tay-Sachs disease is a rare genetic disorder in which little or no hexosaminidase A (hex A) enzyme is produced by the body. Hex A is necessary to break down normal fatty compounds (called gangliosides) in the body cells. When these fatty compounds are not broken down, they gradually accumulate and damage brain and nerve cells, making the cells unable to function properly.

There are two forms of Tay-Sachs disease:

• In the classical or infantile form (the most common type), the body produces no hex A. This form of the disease develops during infancy.
• In late-onset Tay-Sachs (LOTS), the body produces some hex A, but lower-than-normal amounts. This form of the disease begins between adolescence and the mid-30s.

What causes Tay-Sachs disease?

Tay-Sachs disease is an autosomal recessive disease. This means that to have the disease, you must inherit a gene for the disease from both parents. If you inherit the gene from only one parent, you are a carrier, meaning that you carry the gene for Tay-Sachs but do not get the disease.

• To inherit the classical or infantile form, you must inherit from both parents the gene that cannot produce hex A (inactive hex A gene).
• In late-onset Tay-Sachs disease (LOTS), the hex A gene is altered so that it produces a small amount of hex A. If you have LOTS, you inherited two late-onset hex A genes or one late-onset and one inactive gene.

What are the symptoms?

A baby with Tay-Sachs disease appears healthy at birth. Symptoms usually first appear 3 to 6 months after birth, beginning with mild motor weakness and occasional twitches of the eye (myoclonic jerks). By 6 to 10 months of age, the baby's motor skills may be lost. After this, the disease progresses rapidly to seizures, blindness, paralysis, and death at age 4 to 5.

In late-onset Tay-Sachs (LOTS), the symptoms may be subtle (such as clumsiness or mood changes) and go unnoticed at first. Later symptoms may include muscle weakness and twitching, slurred speech, impaired thinking and reasoning, and mental disorders. The life expectancy for a person with LOTS is not known because this condition has only recently been recognized. Depending on the severity of the symptoms, the person may live as long as someone who does not have Tay-Sachs disease.

How is Tay-Sachs disease diagnosed?

A physical examination and a blood test to measure the level of hex A is used to diagnose and screen for Tay-Sachs disease. A positive Tay-Sachs screen blood test may need to be confirmed with other genetic tests.

How is it treated?

Treatment for Tay-Sachs disease focuses on controlling symptoms and preparing for the course of the disease. There is no cure for Tay-Sachs disease. Additional personal and family support measures may be needed as the disease progresses.

How can Tay-Sachs disease be prevented?

If either you or your partner is Ashkenazi Jew or of French-Canadian or Cajun descent or has a family history of Tay-Sachs disease, that person needs to be tested for the Tay-Sachs trait. If that person tests positive, the partner also needs to be tested. If both of you test positive, you should consider genetic counseling before having children.

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