Tay-sachs , Family Planning Options And Preimplantation Genetic Diagnosis (pgd)

If you've had a child or family member affected with Tay-Sachs disease, or if you and your partner are both known Tay-Sachs carriers, you may have wondered about the options available to help you have children free of this condition. Tay-Sachs disease is a inherited condition with onset in infancy which causes progressive neurological degeneration until death, usually by age three or four. Current, there is no treatment or cure. Tay-Sachs disease is inherited in an autosomal recessive manner. This means that couples in which both members are Tay-Sachs carriers have a 25%, or 1 in 4, chance with each pregnancy to have a child who inherits two copies of the Tay-Sachs gene mutation - one from each parent - and will develop the disease. Tay-Sachs is more common in the Ashkenazi Jewish population with one in every 3600 babies being affected and one in every 30 individuals of this ethnic background being healthy carriers for this condition.
Couples may learn of their risk to have a child with Tay-Sachs because of:
Family History: A previous child or other family member was diagnosed with the disease.
Genetic Carrier Testing: Both members of the couple are found to carry mutations within the gene that causes the disease during routine genetic carrier testing.
When a couple wishing to be parents learns they are at increased risk to have a child with Tay-Sachs disease and they want to reduce the chances of passing this condition onto their children, the following options may be considered:
Natural conception with the 25% chance that the baby will have Tay-Sachs
Natural conception with the option of prenatal diagnosis during pregnancy to determine whether the fetus has the disease
Adoption
Use of a sperm or egg donor who is known to not be a Tay-Sachs carrier to prevent passing on the disorder
Preimplantation Genetic Diagnosis (PGD) with in vitro fertilization (IVF) to choose embryos without the disease for transfer to the mother's uterus
Traditionally, couples at risk to have children with Tay-Sachs disease have either chosen to embark on a natural pregnancy with the 25% chance to have a child with the condition or have decided to adopt. Another option, available since the 1980s, includes undergoing prenatal diagnosis during each pregnancy to confirm that the fetus does not have Tay-Sachs disease. However, if the fetus is found to be affected, nothing can be done to treat the condition and the couple may be faced with difficult decisions during pregnancy. Some couples prefer to explore other family planning options rather than take this chance. For some couples, using either a sperm or egg donor who is confirmed to be a non-carrier is an effective way to have a child without Tay-Sachs disease. For couples searching for other ways to have their own biological children, a testing method called preimplantation genetic diagnosis (PGD) may be a good choice.

Preimplantation Genetic Diagnosis, or PGD and Tay-Sachs
Preimplantation Genetic Diagnosis, or PGD, is a specialized laboratory test used during in vitro fertilization (IVF). PGD allows people who are affected with or who are carriers of a specific inherited disorder the chance of having children free of that particular condition. PGD has been used since the mid-1990s by couples who are at known risk for having children with Tay-Sachs disease.
PGD is always done in conjunction with IVF - a procedure in which the woman's eggs are stimulated to develop, then removed and fertilized by the man's sperm outside the body. When the embryos reach a certain size, one or more cells are removed from each embryo and tested in a PGD lab for the mutation(s) present in the family. Once the gene mutation status of each embryo is determined, the parents and their IVF doctor then decide which embryos they wish to transfer to the woman's uterus.
PGD has been used by couples at risk to pass on specific genetic diseases for almost 20 years. There are a number of PGD laboratories nationwide that currently offer testing for many different single gene disorders, including Tay-Sachs. Most PGD labs can also develop 'custom' PGD tests for families with rare genetic conditions or mutations.
Recently, newer PGD methods have allowed testing for chromosome abnormalities - missing or extra chromosomes that would either cause miscarriage or the birth of a baby with a chromosome syndrome such as Down syndrome - at the same time as testing for a single gene disorder such as Tay-Sachs disease. When couples transfer embryos with normal chromosome results on PGD, the implantation rates may be higher and the miscarriage rates may be lower than with traditional PGD methods that test only for the single gene disorder without evaluating the chromosome number at the same time.

By: Barbara Pettersen

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Barbara Pettersen, MS, CGC - Manager, Genetic Counseling Services Gene Security Network (GSN) Barbara Pettersen is a board certified genetic counselor who has worked in the field of clinical genetics for over 26 years. She is using her expertise in PGD at GSN to help families in their quest to have children free of serious genetic conditions. In addition, she has a broad background of experience in prenatal, pediatric and adult ge