Q: I read a wonderful story about how PGD (preimplantation genetic diagnosis) was used to create a sibling to help a child who needed a perfect bone marrow match to treat her rare disease. It’s hard to argue with that logic, but I’ve also read that PGD could be used in the future to let parents pick a baby’s gender or even other characteristics, such as eye and hair color. Is that true? Have you any experience with PGD and if so, what are the perks and when would an average couple want to consider it?
A: Our IVF laboratory in Atlanta has extensive experience with PGD. In fact, we were one of the first laboratories in this country to offer this service to patients. I frequently find myself in the position of counseling patients about the pros and cons of this technology to help them decide whether PGD is something they would want to consider. PGD is wonderful technology if used appropriately.
First, PGD requires IVF. Once the embryos are created, they are allowed to develop for three days until they are at the six-to-eight cell stage. At this point, one cell is removed from each embryo (embryo biopsy) for testing (which can take one-to-two days). The embryos are returned to the incubator until testing is complete, when the best embryos are selected for transfer to the mother’s uterus and hopefully a pregnancy ensues (no guarantees of course). Additional good quality embryos can be frozen for later use.
PGD should never be done without good reason. One should weigh carefully the benefits versus the risks of the procedure before deciding to do PGD. Although most good quality embryos tolerate embryo biopsy very well, some embryos may be slightly damaged by the biopsy procedure so that they slow in their development or stop altogether and cannot be used at all.
PGD is not used to create “designer babies.” PGD, at this moment, cannot determine eye or hair color and it will not be able to do so in the foreseeable future. Yes, it can tell you the sex of the embryo, but what PGD can do best is help people have healthy babies. Most of the time when PGD is done, it is done to detect abnormalities in the embryo. The removed cell is either tested for aneuploidy (extra or absent chromosomes) by FISH (fluorescent in situ hybridization) or for single gene defects by PCR (polymerase chain reaction) technology. Many inherited diseases can be detected in this way.
Women who might want to consider aneuploidy testing are older women who are at increased risk for maternal age-related genetic abnormalities and who do not want to be faced with a decision to terminate an abnormal pregnancy or have an abnormal child. Women of any age with a history of repeated miscarriage should consider aneuploidy testing because most miscarriages occur because the conceptus is chromosomally abnormal. PGD for them can select the best embryos for transfer and can lower their risk of a subsequent miscarriage.
Couples with a family history of sex-linked diseases or of inherited diseases where an abnormal gene has been identified as the cause of the disease (there are hundreds of these identified to date) should consider PGD to improve their chances of having a healthy baby. A family history of sex-linked diseases like hemophilia or retinitis pigmentosa, where the males are affected but the females are carriers would be a good reason to use sex selection and preferentially transfer female embryos because the little girls would be normal (but possibly carriers) while the boys would potentially have the disease.
The story you read about where a sibling was created using PGD for a child with a rare disease could have been a child with Fanconi’s anemia. We have seen a number of these families in our IVF center. Fanconi’s anemia is a rare inherited disease where the child may die without a bone marrow transplant. In these cases you must search for embryos that not only are free of the bad gene but they must also be an HLA match for the affected child in order to make it possible to do the bone marrow transplant.
