Having children without CMT

Preimplantation genetic diagnosis (PGD)
Can a woman who has CMT make sure she has children without CMT?
A woman writes to the Genetics Department at Baylor College of Medicine in Texas via e-mail:
"I am currently trying to get as much information on the subject of prenatal gene testing (and am not even sure if that is the correct term) as I possibly can. Perhaps there is some information that you may have that will prove helpful. I am a 28-year-old female with Charcot-Marie-Tooth disease. I have not been formally tested for a specific "type." As far as I know, my grandmother has CMT. She had four children (all boys); three of them have CMT. One of them is my father. He has three children. Two of us have CMT, both girls. My brother is not affected.

Question: Can I have children without CMT? Is there such a thing as testing for the CMT, by way of in-vitro, before I am actually pregnant, and only being inseminated with "children" without CMT? Or is this just science fiction?
"I understand that there is a 50% chance if I just "wing it." Unfortunately, I don't like the odds of a coin toss."
Answer: I am one of the genetic counsellors here at Baylor. In response to your questions: Yes, it is possible in some cases to have a pregnancy without CMT other than the 50/50 chance if you just "wing it." This is not science fiction. We refer to this testing as preimplantation genetic diagnosis (PGD) and we have doctors here at Baylor who will do this type of testing. We are just one of several centers in this country that perform PGD.

PGD is performed by going through in-vitro fertilization (IVF), and when the embryo is at the 6-8 cell stage, a single cell is removed for genetic testing. How the genetic testing is performed depends on what we are testing for. Based on the family history information you provided, the CMT in your family could be either autosomal dominant or X-linked. Have you been seen by a geneticist or had genetic testing? There are several different genetic forms of CMT. I recommend that you see a geneticist to clarify the type of CMT in your family.

Our preimplantation genetic diagnostic team currently offers PGD for couples where the man has X-linked dominant CMT by determining the sex of the embryos and only implanting male embryos because male offspring will not have X-linked CMT. If you have the X-linked form, this means that all of your children (sons and daughters) would have a 50% chance of inheriting your X chromosome with the CMT gene and thus would also have CMT. It may be possible for genetic testing to determine which X chromosome was passed to an embryo, but I would have to do some further investigating.

In summary, PGD may be a possible option for you, but we would first need to know what type of CMT you have. If you are interested in more information on preimplantation genetic diagnosis (PGD) to ensure that your child will not have CMT1A or HNPP contact: Noelle R. Agan, M.S., Genetic Counsellor; Tel: (713) 798-4363.

If you are already pregnant and want to know if the child will have CMT
by Lisa G. Shaffer, Ph.D., Associate Professor, Department of Molecular and Human Genetics; Director, Kleberg Cytogenetics Laboratory, Baylor College of Medicine, Houston, Texas, U.S.A.

"We have been performing CMT diagnosis in amniocentesis samples since the spring of 1996. Since January 1998, we have been performing CMT testing in CVS specimens. The test is reliable and fast. We can have both the cytogenetic (chromosome) results and fluorescence in situ hybridization (FISH) CMT results to the genetic counsellor or physician within 10 days.

"We require one of the following before we will do a prenatal test for CMT1A or the 1.5 Mb deletion associated with HNPP: 1) the molecular results from Athena (Athena Diagnostics, Four Biotech Park, 377 Plantation St., Worcester, MA 01605, U.S.A.; tel: 1-800-394-4493) will be sent to us for review on the affected parent; 2) FISH was performed on the affected parent in our laboratory; 3) FISH is being sent on the affected parent for screening in our laboratory, prior to or concurrent with submitting the prenatal specimen.

"We prefer to discuss individual cases with genetic counsellors and physicians and not the patient. I do not feel that genetic counselling is effective communication over the telephone and prefer that the patient is in contact with a specialist in the field."

Note: Remember this only works on CMT1A or HNPP right now. For more information on prenatal testing to see if your unborn child has CMT1A or HNPP, please get in touch with Baylor College of Medicine, Kleberg Cytogenetics Laboratory, One Baylor Plaza, Room 15E, Houston, Texas 77030, U.S.A.; Tel: 800-411-GENE in the U.S.A. or (713) 798-4984; Fax: (713) 798-3147; e-mail: kcl@bcm.tmc.edu and website: www.bcm.tmc.edu/medgen/