Tay-Sachs Disease

Examinations and Tests

If your baby is suspected of having Tay-Sachs disease, a physical examination may reveal or confirm symptoms of the disease. A blood test (Tay-Sachs screen test) can determine whether your baby's body is producing the enzyme hexosaminidase A. The blood sample can be taken from a vein or from the umbilical cord immediately after birth.

If you are pregnant and are at risk for having a child with Tay-Sachs disease, the Tay-Sachs screen test can be done on a blood sample collected from the placenta during chorionic villus sampling or on a sample of amniotic fluid collected during amniocentesis. For more information, see the medical tests Amniocentesis and Chorionic Villus Sampling.

The Tay-Sachs screen test is also used to confirm late-onset Tay-Sachs disease in a teen or adult with symptoms of the disease.

A positive Tay-Sachs test may need to be confirmed with other genetic tests. For more information, see the medical test Genetic Test.

Screening for carriers

Knowing whether you are a carrier of Tay-Sachs disease is important, because Tay-Sachs is an autosomal recessive disease. If you are a carrier, you have the Tay-Sachs trait but not the disease. You have one chromosome that produces hexosaminidase A and one that does not produce this enzyme. Your body probably makes about 50% of the normal level of hex A, which prevents you from getting the disease; however, you can pass the trait on to your children. If both you and your spouse are carriers, there is a 1-in-4 chance (25%) that any child you have will have Tay-Sachs disease.

If you are considering having a child, the Canadian College of Medical Geneticists and the Society of Obstetricians and Gynaecologists of Canada recommend that:¹

• Both prospective parents be screened if both of you are Ashkenazi Jews or of French-Canadian or Cajun descent or have a family history of the disease. If both of you test positive as carriers, you should consider genetic counselling.
• You or your partner be screened if either of you is an Ashkenazi Jew or of French-Canadian or Cajun descent or has a family history of the disease. If one of you tests positive for the trait, the other partner should be screened.

Some provinces in Canada offer Tay-Sachs screening to high school students of Ashkenazi Jewish descent. Later, when women who are carriers are considering pregnancy, their partners should also be tested.²

Recently, one study compared testing for hexosaminidase A with testing DNA directly for Tay-Sachs disease. Evidence indicates that DNA testing is the most cost-effective and efficient approach to carrier screening.³

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Author:	Carrie Henley Sabra L. Katz-Wise	Last Updated: June 20, 2006
Medical Review:	Adam Husney, MD - Family Medicine Michael J. Sexton, MD - Pediatrics Renee H. Martin, PhD - Medical Genetics
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