Preimplantation Genetic Diagnosis and Screening
It is also possible to screen embryos for genes that raise the risk of cancer—primarily breast, ovarian, and colon—in adulthood. We know this is being done in England today, where regulators ruled last year to allow it. The questions are a bit different with this issue, as I see it, because genotype in this case does not accurately predict phenotype. Having the BRCA1 or BRCA2 gene mutation does not mean, for instance, that a person will develop breast or ovarian cancer. So the question really is whether we should be testing embryos for a disease that may never occur.
As in other ethical debates, we must listen to all points of view. Many couples have watched multiple family members die from colon cancer or breast cancer and have decided that enough is enough, whereas other couples who are testing for HLA matching have a child with an incurable, often fatal disease. These couples know there is no such thing as a perfect baby. All they want is to have the A and the G and the T and the C in the right places, or to save their child while having the chance to have another healthy baby to love as well.
Most clinics have ethics teams to develop policies that address these issues and to describe which indications for preimplantation genetics are acceptable and which are not. Most clinics allow the use of technology for finding cancer genes and for HLA matching, for instance, but not for selecting gender.
Studies following children after IVF and preimplantation genetics that have been done in Europe—where the type of medical system allows investigators to effectively track patients for longer-term outcomes—are better than those done in the United States. Clearly, safety and good outcomes have been demonstrated. Thousands and thousands of babies have been born after having undergone IVF and PGS or PGS, with no evidence of birth defects.
Still, experts in the United States have been designing a database—a prospective registry of sorts—that, when implemented, will collect data on the use of preimplantation genetics, primarily regarding how much is being done and for what ends the technology is being used. Such data will help us to further understand and guide this fast-growing facet of reproductive medicine.
A human 8-cell embryo produced routinely in an IVF laboratory is undergoing the biopsy of one blastomere (cell) for testing. Courtesy Dr. Mark R. Hughes
The Quest for Prenatal Evaluation
The quest for fetal and embryonic evaluation has been of great interest to many scientists, physicians, parents, and members of the lay public. It has eventuated into the well-established field of prenatal diagnosis.
The focus, for the most part, has been on gleaning information during the early and midtrimester periods of pregnancy. Such evaluation has been found most useful in providing reassurance to parents when anomalies are excluded, or—under those uncommon circumstances when a diagnosis is made prenatally—in allowing parents and physicians to create appropriate medical and social strategies to deal with these diagnoses.
Despite the benefits afforded by prenatal diagnosis, there remains a subset of the potentially reproductive population for whom conceiving and delivering an abnormal child is not a rare event, but may in fact have a high degree of predictability. These aspiring parents have had to choose among high-risk pregnancy, nonconception, adoption, or egg or sperm donors.
Most recently, however, these patients and their physicians have been able to exploit the new technology of preimplantation genetic diagnosis. This is a rapidly expanding field that has the potential to make a significant difference in the lives of patients who could not otherwise be anywhere near certain that they would deliver a healthy, normal child.
The technology affords us a wide range of possibilities, both now and in the future, but it also presents a number of challenges, including ethical issues, financial coverage issues, and issues concerning the actual availability of the services to select populations and individuals.
This all makes preimplantation genetics quite a complex topic, with great positive potential and a great many implications and potential hurdles and obstacles, all of which must be discussed and deliberated.
It is for this reason that we have invited Dr. Mark R. Hughes, a leading international scholar in the area of preimplantation diagnosis and one of the pioneers of this technology, to serve as the guest author of this month's Master Class.
Currently, Dr. Hughes is the director of the Genesis Genetics Institute in Detroit. He previously served on the faculty of the schools of medicine at Baylor College of Medicine, Georgetown University, and Wayne State University, and was a member of the founding group of the Human Genome Institute at the National Institutes of Health.
