Tay-Sachs Test
The test for Tay-Sachs disease measures the amount of an enzyme called hexosaminidase A (hex A) in the blood. Hex A breaks down fatty substances in the brain and nerves. Tay-Sachs is an inherited disease in which the body does not break down fatty substances as it should, so the fatty substances collect in the body and damage brain and nerve cells.
Normally a child inherits one gene from each parent that tells the body to make hex A. If you inherit:
- A pair of genes that does not tell the body to make hex A, you have Tay-Sachs disease.
- One gene that tells the body to make hex A and one that does not, you are a Tay-Sachs carrier. Because your body still makes enough hex A, you do not have the disease. But you can pass the gene to your children. If both parents are carriers, there is a 1-in-4 chance (25%) that any child they have will have Tay-Sachs disease.
A Tay-Sachs test may also measure the amount of another enzyme, called hexosaminidase B. People who cannot make either hex A or B have a rare, more serious condition called Sandhoff's disease.
The Tay-Sachs test is usually done on blood taken from a vein or from the umbilical cord right after birth. It can also be done on a sample of amniotic fluid (collected during amniocentesis) or on special cells in the placenta (collected during chorionic villus sampling).
Why It Is Done
A test to measure hexosaminidase A is done to:
- See whether a newborn has Tay-Sachs disease.
- Find Tay-Sachs carriers. People of Ashkenazi Jewish, French-Canadian, or Cajun descent who have a family history of Tay-Sachs disease or who live in a community or population with a high amount of Tay-Sachs disease may want to be tested.
- See whether an unborn baby (fetus) has Tay-Sachs disease. This is done early in pregnancy by amniocentesis or chorionic villus sampling.
How To Prepare
You do not need to do anything before having this test. If you are having this test to see whether you are a Tay-Sachs carrier, you should tell your doctor if you have had a blood transfusion in the past 3 months.
Discuss with your doctor any
concerns you have about the need for the test, its risks, how it will be done,
or what the results may mean. To help you understand the importance of this
test, fill out the
medical test information form 
(What is a PDF document?).
How It Is Done
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
WebMD Medical Reference from Healthwise
-
1
-
2
-
3
-
4
-
5
-
6
-
7
-
8
-
9
-
10
-
11
-
12
Sleep expert helps new moms get more rest.
