Tay-Sachs Disease

WHAT YOU SHOULD KNOW

Tay-Sachs disease is a rare, fatal, hereditary disorder in which large and damaging quantities of a fatty substance called ganglioside GM ₂ accumulate in the brain, causing gradual deterioration. The disease strikes 1 in 3,600 infants of Eastern European (Ashkenazi) Jewish or French Canadian decent, and ends in death by age 3 or 4. In extremely rare cases, the disease develops later in life.

Causes

This disease is caused by the absence of a digestive enzyme called hexosaminidase A (hex A), which is needed to break down certain fatty compounds in the brain. When the enzyme is lacking, a gradual buildup of these compounds quickly begins destroying nerve cells. In the later-developing forms of the disease—known as juvenile hex A, chronic hex A, and adult-onset hex A—the victim suffers from low levels of the enzyme, rather than its complete absence.

A child will develop this disorder only if both parents are Tay-Sachs carriers. In such individuals, one of the two genes that trigger production of hex A is defective. Although the carriers themselves do not have the disease or any of its symptoms, there is a 25 percent chance that any child they produce will inherit a defective hex A gene from each of them, and, with no normal hex A genes, succumb to the disease. (There is a 50 percent chance that the child will inherit one normal hex A gene and one Tay-Sachs gene and, like his parents, become a Tay-Sachs carrier. There is also a 25 percent chance that the child will inherit a normal hex A gene from each parent and be completely free of the disease.)

If only one parent is a carrier, the child is certain to receive at least one normal hex A gene and thus be spared from disease. However, he has a 50 percent chance of inheriting one defective gene and becoming a carrier.

Signs/Symptoms

The first signs of Tay-Sachs disease appear during the first 4 to 6 months of life. The disease typically starts with a decline in motor skills and muscle tone. Later the child suffers paralysis, dementia, blindness, seizures, an enlarged head, an inability to swallow, and cherry-colored spots in the retina of the eye. Symptoms become progressively worse until death occurs.

In juvenile hex A, the disease does not appear until the child is between two and five years old. The symptoms are the same as those of Tay-Sachs, but the disease progresses much more slowly and death is usually delayed until the early to mid-teenage years.

In chronic and adult-onset forms of hex A, symptoms are much milder. They typically include slurred speech, muscle weakness and cramps, tremors, and an unsteady gait. In some cases, mental illness ensues as well. Vision and hearing may remain intact until the final stages of the disease. Victims usually survive into their twenties or early thirties.

Care

At present, there is no cure or treatment for Tay-Sachs disease. Researchers hope to someday conquer this genetic disease with advanced forms of gene therapy.

WHAT YOU SHOULD KNOW

Although there is little that can be done to prolong or enhance the life of a child stricken with Tay-Sachs disease, there are several steps you can take to minimize the risk of giving life to such a child.

• Have genetic testing done prior to conception, especially if you or your partner are of Jewish decent. There are various types of blood tests, including DNA-based genetic testing, that can determine whether you are a carrier of the defective Tay-Sachs gene. Additional testing can even diagnose which of the four types of the Tay-Sachs gene one carries.
• Talk with your doctor prior to the tests and discuss the ways you can respond to each possible result. Testing is available at genetic service centers or clinics.
• If pregnancy occurs, you can get prenatal testing to confirm the presence of hex A in the unborn child.
• For more information, contact the National Tay-Sachs and Allied Diseases Association at 800-90-NTSAD or visit its website at www.ntsad.org.

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