Family planning options for HD-free kids: Prenatal and preconception options

Wednesday, July 29, 2015

 

By Shawna Feely, MS, CGC
UI HDSA COE Genetic Counselor, and
Carly Siskind, MS, LCGC
Stanford School of Medicine, Neuromuscular Disorders Program

“Will my kids have what I have?” 

Baby 2
Several family planning options exist to prevent 
having a child at risk for HD

This is a common question in genetic counseling. Sometimes this question comes after the kids are already grown, in which case we know the risk is 50-50 that someone has Huntington disease. But in other cases, this question comes before pregnancy, which leads to a conversation about reproductive options.

In this article, we will review the available options for people who would like to take steps to prevent passing HD on to future generations. Once again, these are personal decisions, and some people pursue these options, while others do not. There is not one right way to do things; it all depends on the individual.It is possible to make family planning decisions to prevent having a child that is at risk for HD. These are very personal decisions, and what is right for one person or family may not be what is right for others. Our job as genetic counselors is to present the available options, and to help the family determine what is best for them. Once a person understands all the options, they are able to make an informed choice, which is what genetic counseling is all about. 

Prenatal options

If a woman is pregnant, the pregnancy can be tested to determine if it has the gene expansion that would cause HD. This can be done in a few ways.

Chorionic Villus Sampling (CVS): CVS is performed between 10 and 12 weeks of pregnancy. A sample of the placenta is taken, either transabdominally with a biopsy needle, or transvaginally with a catheter. The cells are taken and tested for the familial gene expansion. Complication rates vary by center and expertise of the person performing the test, but are usually quoted between 1-in-100 to 1-in-300. Complications can include miscarriage. 

Amniocentesis: This test is performed after 15 weeks of pregnancy, in the second trimester. A sample of the fluid that surrounds the pregnancy (amniotic fluid) is taken, and the cells in the fluid are analyzed for the familial gene expansion. The complication rates for amniocentesis are usually lower than CVS but also vary by center and level of expertise. These are usually quoted between 1-in-200 to 1-in-1000. 

Non-invasive prenatal diagnosis (NIPD): This is not readily available for HD but could be within the next couple of years. A sample of the mother’s blood (known as maternal blood) is taken through a regular blood draw. The sample is analyzed for cell-free fetal DNA, which is essentially DNA from the pregnancy that has passed the placental barrier into maternal blood. The lab would look for the presence of the gene expansion that causes HD. If dad is the HD-affected individual, the presence of the gene expansion in mom’s blood would be very suggestive of an affected pregnancy. If mom is the affected individual, the lab would analyze the proportion of gene expansion versus non-gene expansion DNA. Currently, this test would likely need to be followed up with one of the more invasive testing methods for confirmation, as it is less accurate.

What a family does with the information from this testing is ultimately up to them, however typically this testing is offered to couples who plan to terminate a pregnancy if it is determined to be affected by HD. These are very difficult and personal decisions, and are discussed extensively with the couple, their genetic counselor, and their doctor. It is not the right option for everyone, but this method can prevent future generations from having HD.

Preconception option

Preimplantation genetic diagnosis (PGD) is available for a woman does not want to have a child at risk for HD and does not want to have to make the decision about terminating a pregnancy. PGD is used in connection with in vitro fertilization (IVF), which is a procedure more commonly used for couples who have difficulty conceiving on their own. In IVF, egg and sperm are combined in a laboratory and grown into embryos. Different labs use different technologies, but once an embryo has a certain number of cells (at least six), between one and ten are removed either by a biopsy, removed chemically or removed by a laser. The DNA from these cells is analyzed for the familial gene expansion. At some labs, for an additional charge, they can also look for another feature, such as chromosome number. So, for example, they can avoid implanting an embryo with an extra chromosome 21, which causes Down syndrome. 

The lab would choose the best embryos that are not affected with HD to be implanted back into the uterus of the mother to carry to term. PGD can be an amazing option for some families, but there are downsides. In order to retrieve the eggs from the woman, she must get hormone shots to stimulate the follicles. The eggs must be removed surgically. A second surgery is then needed to reimplant the embryos. There is no guarantee that the embryo will implant when reentered into the uterus, so an additional cycle may be needed. Each cycle of IVF tends to cost $10,000¬–$20,000, and not all insurances cover it. Furthermore, each PGD is often another $3,000–$5,000. People who use IVF for non-infertility reasons (e.g., PGD for HD), however, do have a higher percentage of success per cycle than those who are using IVF because of infertility. Finally, many centers would suggest following up PGD with a CVS or amniocentesis to ensure that the embryo implanted really was free of the gene expansion causing HD.

All of these options are available for couples who know the affected parents’ gene status. They are also available if someone is at risk for HD, but does not want to know their own status. This is called non-disclosure testing. For example, an individual can go through PGD to prevent passing HD on, but they are not informed if any of the embryos are affected by HD. They are only told if the embryos are healthy or unhealthy. The embryos could be unhealthy for a variety of reasons, therefore, the person at risk doesn’t learn his or her gene status but can still have their own biological children and prevent passing HD on to them. Your local genetic counselor (find a genetic counselor through the National Society of Genetic Counselors) would be happy to go over the specifics of these options in more detail. These are very personal decisions and only the family can know if one of these options is right for them.
 
Click here to read about further options involving adoption and using sperm or egg donors.