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.
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.
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?).
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.
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.
There is very little chance of a problem from
having a blood sample taken from a vein.
You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.
In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
Reasons you may not be able to
have the test or why the results may not be helpful include:
Having a recent
blood transfusion. If you have a blood transfusion
from a blood donor who has normal levels of hexosaminidase A, your level may
temporarily be higher than usual.
A positive Tay-Sachs test may need to be
confirmed with other genetic tests. For more information, see the medical test
Genetic Test.
If you are pregnant or use birth control pills, your doctor would
test the hexosaminidase A (hex A) amount in your
white blood cells.
People who have a high
chance of being a
carrier of Tay-Sachs may want to have a blood test to
see whether they are carriers before they have children. People of Ashkenazi
Jewish or French-Canadian 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.
Genetic counseling is available for people who have
the disease or are carriers.
If the parents of an unborn baby
(fetus) are Tay-Sachs carriers, the following tests
can be done to see if the baby has the disease.
An
amniocentesis checks a sample of
amniotic fluid and is usually done between the 14th
and 18th weeks of pregnancy. For more information, see the medical test
Amniocentesis.
This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.
