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.

The Tay-Sachs gene is most common in people of Ashkenazi Jewish descent. About 1 out of 30 people in this population is a carrier of the disease.¹² People of French-Canadian descent from the East Saint Lawrence River Valley of Quebec and people of Cajun descent in Louisiana are also at a higher risk than the general population.

What causes Tay-Sachs disease?

Tay-Sachs disease is an autosomal recessive disease. If you inherit from both parents a changed (mutated) gene that can cause Tay-Sachs, you will get the disease. 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 exam and a blood test to measure the level of hex A is used to diagnose Tay-Sachs disease. A positive Tay-Sachs screen blood test may need to be confirmed with other genetic tests.

How is it treated?