The revolution in genomics is not only changing the way people who carry genetic diseases have children. It is starting to make its way into everyone else’s family planning, too.
As the ability to analyze big data grows, doctors can now tell with much more accuracy and ease whether two people are carriers of a huge catalog of genetic diseases before the couple starts trying to have a child. For those who test positive, in vitro fertilization and improved techniques for screening embryos can minimize a couple’s chances of having a child with inherited diseases.
If one person has a recessive gene for a disease, it doesn’t mean they will pass it on to their children. But if both parents have the same gene, the odds are greatly increased.
A decade ago, for the small population of parents known to be at risk, genetic screening and screening of embryos would cost around $5,000 and could only look for a handful of inherited illnesses. Now, tests from a half-dozen companies can identify hundreds of illnesses for far less.
One test, from Sema4, part of the Mount Sinai Health System in New York, identifies 281 separate illnesses and costs only $299. Some of those diseases are fairly common. For example, 1 in 20 people carries the gene for cystic fibrosis, a disease that limits the ability to breathe. Carrier Check, also developed by Sema4 and by genomics startup Helix, allows women to test their DNA for 67 possible hereditary diseases with a consumer saliva kit at home.
Screening of genetic material in embryos has made important advances as well. In the past, couples who feared passing along a genetic mutation could opt either not to have children or to conceive a child and have the fetus tested for birth defects. Positive amniocentesis tests often resulted in abortions. Now, advances in technology and in affordability have made embryonic genetic screening more accurate and accessible to many more people. Also, with in vitro fertilization, an egg is fertilized in a petri dish and then examined after a day. If it carries the disease, it is not implanted.
Owen Davis, a professor of reproductive medicine at Weill Cornell Medical Center in New York, says there is no question that the technology for screening embryos—called preimplantation genetic diagnosis, or PGD—has improved. “The cost has come down dramatically, and the benefit of PGD is clear,” he says. In addition, “many more people are getting more broadly screened when they go for preconception counseling with their OB-GYN.”
These recent advances create a clearer pathway toward having a healthy child. Indeed, genetic screening is becoming a more routine part of prenatal care, even for those who don’t have a genetic disease in the family. The idea that screening should be provided to women before they get pregnant is promoted by testing companies and increasingly taking hold among doctors.
The growing potency and popularity of such screening, however, does pose important ethical questions. Some tests screen for genetic diseases that don’t develop, if at all, until adulthood, and sometimes genetic flaws are discovered that have uncertain significance.
Some of the conditions being tested for are extremely rare and not fatal, says Arthur Caplan, director of medical ethics at NYU Langone Medical Center. There is also a move to test for diseases such as ovarian cancer and breast cancer, which, while currently devastating, may have a cure in coming decades.
“You don’t want to screen for a disease for which it’s reasonable to predict cures,” Dr. Caplan says.
Also, Dr. Caplan says, the increased screening and use of in vitro fertilization has led to a larger number of embryos being discarded. Critics have long contended that by discarding embryos with certain diseases, parents are unfairly victimizing people who have the condition.
To help couples understand the odds and the risks, counseling is available before and after screening tests. According to Eric Schadt, chief executive of Sema4, 70% of the women tested are positive as a carrier for one of the 281 disorders for which they are screened. Dr. Schadt, who has a Ph.D. in biomathematics, says a genetic counselor then advises women to have their partner tested as well because the chances they will both test positive are fairly small.
“If they test positive as well, then we provide more rigorous counseling to say, ‘Your chances are now 1 in 4 of having a baby that’s affected by this disorder, and IVF becomes an option,’ ” Dr. Schadt says
In a few cases, today’s more-advanced genetic screening of embryos has helped doctors treat and cure diseases before a child is born. Parents of an embryo in which the gene mutation that causes sickle-cell anemia is found, for example, can use in vitro fertilization to give birth to a second child, sometimes referred to as a savior sibling, who doesn’t have the disease, but is identical genetically to the first child. Stem cells are harvested from the placenta and implanted in the bone marrow of the first child, curing the sickle cell.
A technological advance on the horizon, meanwhile, could further help parents who carry genes for the disease. The gene-editing process known as Crispr was shown in a recent study to be capable of removing a gene defect from a fertilized egg.
While the practical use of this type of gene editing is at least a decade away, when it becomes widely available, parents will no longer have to discard embryos that are carrying genes for diseases such as cystic fibrosis. Instead, an embryo can be repaired, with the added benefit that the gene will disappear forever from the genetic information passed on to future generations.
Brian P. McDonough, MD, FAAFPPeer
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