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Tay-Sachs Disease

Does this test have other names?

Tay-Sachs carrier screening, Tay-Sachs prenatal testing, Tay-Sachs disease DNA analysis

What is this test?

This test looks for specific genetic changes in a sample of your blood or, if you're already pregnant, of the fetus' blood. These genetic mutations cause most cases of Tay-Sachs disease.

People with Tay-Sachs disease have low levels of the Hex A enzyme. This can cause a fatty substance called GM2 ganglioside to build up in cells, especially in brain cells.

Symptoms of the disease start in infancy. Babies who have Tay-Sachs develop trouble moving, seizures, and blindness. Children with the disease typically die before age 6.

This DNA test can find out whether parents or potential parents are carriers of the disease. It can also be used to see if a fetus has the condition.

Many people of Ashkenazi, or Eastern European Jewish descent are carriers for the disease. This means they have gene mutations that can cause the disease in a child. About one in 27 American Jews are carriers. If both parents are carriers, a child has a 25 percent chance of getting the disease and a 50 percent chance of being a carrier. Carriers do not have symptoms of the disease but can pass the defective gene to their own children.

This DNA test checks for three or more specific genetic mutations. Testing can identify nearly all carriers.

Before having this test, discuss your family background with your health care provider or a genetic counselor to determine which type of testing you and your partner should have.

Why do I need this test?

You may have this test to check whether you are a Tay-Sachs carrier. If you are pregnant, both you and your partner can be tested. If both you and your partner are known carriers, DNA testing can diagnose Tay-Sachs disease in the fetus.

What other tests might I have along with this test?

Your doctor may also order blood tests to measure Hex A and Hex B enzymes to find out whether you are a carrier.

Your doctor may also order screening for cystic fibrosis, Canavan disease, and familial dysautonomia, especially if you are of Ashkenazi Jewish descent.

If you are not of Ashkenazi Jewish descent, your doctor may also order a screening test for an additional DNA mutation that has been linked to Tay-Sachs in other populations.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal results are negative, meaning that no genetic mutations have been found and that you aren't a carrier for Tay-Sachs disease. A positive result means that the genetic mutations have been found and that you are a carrier.

Normal results for prenatal testing are negative, meaning that no genetic mutations have been found and that your fetus does not have Tay-Sachs disease. A positive result means that the genetic mutations have been found and that your fetus does have the disease. A genetic counselor or your health care provider can discuss what these results mean for you and your child.

How is this test done?

For carrier screening, the test requires a blood sample, which is drawn through a needle from a vein in your arm.

Testing the fetus during pregnancy requires one of these procedures:

  • Amniocentesis, in which the doctor takes a sample of amniotic fluid from around the baby

  • Chorionic villus sampling, in which the doctor takes a sample of cells from the placenta

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

Risks from amniocentesis include:

  • Cramping and vaginal bleeding

  • Fetal injuries

  • Amniotic fluid leakage

  • Infections, such as hepatitis or HIV, spreading from you to your fetus

  • Slight risk of miscarriage

Risks from chorionic villus sampling include:

  • Miscarriage

  • Vaginal bleeding

  • Leaking of fetal blood into your bloodstream, which may cause problems in later pregnancies

What might affect my test results?

The test is not 100 percent accurate, so you may have a false-negative result. This means you are a carrier even though the test results came back negative.

How do I get ready for this test?

You don't need to prepare for the blood test. If you are having an amniocentesis or chorionic villus sampling procedure, you may need to avoid sex or exercise on the day of the test.