The First Article in a Series
By Shawna Feely, MS, CGC, and Carly Siskind, MS, LCGC
A common question in genetic counseling is, “Will my kids have CMT?” Sometimes this question comes after the kids are already grown, in which case the answer is based on the type of CMT someone has. But in other cases, this question comes before someone is pregnant. In these cases, we have a conversation about reproductive options.
If the genetic type of CMT is known, it is possible to find out if a child will be affected or make decisions to not have a child if he or she would be affected. 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 options that are available, and to help the family determine what is best for them.
If a woman is pregnant, the pregnancy can be tested to determine if it has the familial mutation that causes CMT. 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 mutation. Complication rates vary by center and expertise of the person performing the test, but are usually quoted at 1 in 100 to 1 in 300. Complications can include miscarriage. Amniocentesis: This test is performed after 15 weeks of pregnancy (second trimester). A sample of the fluid that surrounds the pregnancy (amniotic fluid) is taken, and the cells found are analyzed for the familial mutation. The complication rates for amnio are usually lower than CVS but also vary by center and expertise. These are usually quoted as 1 in 200 to 1 in 1000. Non-invasive prenatal diagnosis (NIPD): This is not readily available for CMT but will be within the next couple of years. A sample of 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 to see if the familial mutation is present in this sample. If dad is the affected individual, the presence of the mutation 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 mutation versus non-mutation DNA. This test would likely need to be followed up with one of the invasive procedures listed above for confirmation.
What a family does with the information from this testing is up to them. Some people want to know so they can plan once the child is born. Other people are very adamant that they do not want to have a child with CMT, and would decide to terminate the pregnancy. These are very difficult decisions.
For a woman considering a pregnancy, preimplantation genetic diagnosis (PGD) is available if someone does not want to have a child affected with CMT 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 6), between one and ten are removed by a biopsy, chemically, or by a laser. The DNA from these cells is amplified and analyzed for the familial mutation. 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 CMT 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 to it. In order to retrieve the eggs from the woman, she must get hormone shots to stimulate the follicles. A surgery must be performed to remove the eggs. A second surgery is then needed to re-implant the embryos. There is no guarantee that the embryo will implant when re-entered into the uterus, so an additional cycle may be needed. Each cycle of IVF tends to run $10,000 to $20,000, and not all insurances cover it, and PGD is often another $3,000 to $5,000. People who use IVF for noninfertility reasons (e.g., PGD for CMT), 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 familial mutation. All of these options are available only for people who know the genetic cause of their CMT. Your local genetic counselor (www.nsgc.org—Find a Genetic Counselor) 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.
[In the next article, Shawna and Carly will discuss options for adoption and for using sperm or egg donors.]