Tay-Sachs disease is an inherited metabolic disorder. Both parents must be carriers in order to have an affected child. Carrier couples have a 25% chance with each pregnancy of conceiving a child with that condition. There is a 50% chance of producing a child who is a carrier like the parents, and a 25% chance that the child will be neither a carrier nor affected with the disease.
Carrier couples need time to review their options and make the necessary decisions about planning and protecting their families. We strongly recommend reviewing your options with a genetic counselor before getting pregnant.
Prenatal tests can diagnose Tay-Sachs disease before birth. Two prenatal diagnostic procedures are available for carrier couples:
1. Chorionic villus sampling (CVS) is a newer technique and is performed earlier in pregnancy, between the 10th and 12th week of pregnancy. The doctor retrieves a sample of cells from the developing placenta (afterbirth), either through a thin tube inserted through the vagina and cervix to the placenta or by inserting a needle through the mother's abdomen. The tissue that is taken contains cells that generally are identical to those of the fetus, and these cells are examined for the presence of Hex-A. CVS only determines whether the fetus is affected or not; CVS cannot determine if the fetus is a carrier.
2. Amniocentesis is a prenatal procedure that involves removing and testing a small quantity of the fluid that bathes the fetus in the uterus. A small sample of the fluid is extracted through a needle guided by ultrasound. This procedure is done at approximately between the 15th and 18th week of pregnancy. Genetic specialists take some of the living cells from the fluid and allow them to reproduce for a week or two. Then they test the cells for chromosomal abnormalities and certain genetic disorders.
Results from prenatal testing takes approximately between 10 days and 3 weeks. CVS usually provides a test answer much sooner than amniocentesis. Generally speaking, if prenatal tests show that Hex-A is present, the baby will not have Tay-Sachs disease. If Hex-A is missing in fetal cells, the infant will have TSD.
OUR EXPERIENCE WITH PRENATAL TESTING
I took a home pregnancy test, which came out positive. We made an appointment for an ultrasound at our local hospital, to check for dates. The ultrasound showed that I was 8 weeks pregnant.
Then, my doctor referred me to a high-risk obstretician at the University of Chicago Hospital. We met with both the OB and a genetic counselor to discuss the options and risks. We were told that it would take a week to 10 days to receive the results of the prenatal test through our local lab. We knew that the Tay-Sachs Prevention Program at Thomas Jefferson University in Philadelphia offered a preliminary assay that was much quicker, so we contacted the program director there and made arrangements to send one portion of the sample there.
I went to the University of Chicago Hospital at the beginning of my 11th week of pregnancy. The doctor performed a prenatal test called a CVS (chorionic villus sampling) and took some tissue from the placenta. The sample was divided into two portions. One portion went to the lab at the University of Chicago Hospital for chromosomal analysis. By prior arrangement, the other portion of the sample was frozen and sent to the Tay-Sachs Prevention Program at Thomas Jefferson University in Philadelphia for enzyme analysis. The second tissue sample was examined for the presence of Hex-A. The following morning, our genetic counselor from University of Chicago called us at 10:00 AM with the results - the preliminary assay indicated that the fetus was unaffected (test cannot determine carrier status, just tells if Hex-A is present). It took about a week to get confirmation of these results.
I continued the rest of my prenatal care with my local doctor. For our own peace-of-mind, we followed the advice of the Tay-Sachs Prevention Program and had our baby tested after birth. When Madison was 9 months old, we had blood drawn and sent to Thomas Jefferson University to be tested. Now we know she does not have Tay-Sachs disease.
For further information, contact:
Tay-Sachs Prevention Program
If the fetus is affected, the family may wish to terminate the pregnancy - that is to say, elect to have a therapeutic abortion. In this way, even at-risk couples can be helped to have children, as many as they wish, who are free of Tay-Sachs Disease.
For those whom termination or therapeutic abortion is not an option, there are alternatives for expanding your family. Interested families should contact their genetic counselor or doctor for more information about their options.
Adoption and Foster Care
Adoption and foster care are other alternatives to explore if you plan to expand your family.
Some families look to assisted reproduction. Your physician can refer you to reproductive specialist for more information about artificial insemination with donor sperm or donor eggs. In this case, the donor would be tested for carrier status.
For carrier couples with known mutations, PGD or pre-implantation genetic diagnosis is possible at a handful of laboratories. In this procedure, the embryos are tested in-vitro for the disease gene. Only embryos without the gene are implanted in the mother's womb.
Before a PGD is performed, a woman takes drugs to stimulate production of her eggs and undergoes surgery to remove the eggs. After fertilization in a laboratory, an opening is made in the covering of the embryo on the third day of development. One or two of the embryo's 8 to 10 developing cells are removed and examined. A biopsy identifies both maternal and paternal genes, so it allows for differentiation of normal, carrier, and disease states.
Can pregnant women be tested as carriers?
Special considerations are involved in carrier testing of pregnant women because the standard biochemical test used to test males and non-pregnant women cannot be used in pregnant women because of changes in serum enzyme levels during pregnancy.
Pregnant women must instead be tested using leukocytes (white blood cells). The leukocyte test is as reliable as the blood serum test, but is considerably more complex and costly.