Tay-Sachs Test

Serum Hexosaminidase A and B

Test Overview

The test for Tay-Sachs disease measures the amount of an enzyme called hexosaminidase A in the blood. Hexosaminidase 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 chromosome from each parent that tells the body to make hexosaminidase A. If you inherit:

• A pair of chromosomes that does not tell the body to make hexosaminidase A, you have Tay-Sachs disease.
• One chromosome that tells the body to make hexosaminidase A and one that does not, you have the Tay-Sachs trait. This means you are a carrier of Tay-Sachs and can pass the trait on to your children. You do not have the disease because your body still makes enough hexosaminidase A. 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 hexosaminidase A or B have a rare, more serious form of Tay-Sachs 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).

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Author:	Jan Nissl, RN, BS	Last Updated April 14, 2006
Medical Review:	Michael J. Sexton, MD - Pediatrics Renee H. Martin, PhD - Medical Genetics
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