Creating babies with three genetic parents may be the next step in preventing disease before a child is born. It may also be the next step in the long debate over how much control is too much in designing your child.
Sometime in 2015, a baby could be born with three parents. Researchers are developing techniques to prevent mitochondrial diseases, which are genetic diseases passed from mother to child. The key is using genetic material from two mothers and one father to create a single healthy baby.
That first three-parent child will probably be born in Great Britain. British researchers have won preliminary approval to develop a technique called mitochondrial transfer to remove mitochondria that cause disease. The United States Food and Drug Administration held hearings on the issue in February, but the panel chose to wait for more information.
“I applaud the British for taking the first step,” fertility expert Dr. Jeffrey Steinberg, founder of The Fertility Institutes in New York and Los Angeles, told Healthline. “The United States is taking a back seat in the development of this newest medical technology that can prevent genetic diseases by changing the genes that cause disease.”
The Newest Test Tube BabiesDesigning babies starts with in vitro fertilization (IVF). The father’s sperm is mixed with the mother’s egg in a laboratory dish. The egg is fertilized, develops into an embryo, and is implanted in the mother’s uterus. Nine months later, the baby is born.
The problem, Steinberg said, is that IVF is slow, difficult, and expensive. What’s more, not all eggs are successfully fertilized and not all embryos are healthy.
Fertility researchers have adapted genetic techniques to screen embryos before implanting them in the mother. This process is called preimplantation genetic diagnosis (PGD).
In the early days of PGD, doctors counted the number of chromosomes in the embryo. Human cells usually contain 23 pairs of chromosomes, or a total of 46. If there are too many chromosomes, or too few, the embryo is likely to die. If it survives to birth, the child is likely to have a serious disease.
A person with three copies of chromosome 21, for example, has Down syndrome. A girl born with just one sex chromosome has Turner syndrome. PGD lets fertility doctors implant only embryos with 46 chromosomes.
More recent genetic technology allows doctors to screen for specific genes. For example, some types of diabetes, called monogenic diabetes, are caused by the mutation of a single gene.
Doctors can screen for more than 400 common genetic diseases today, Steinberg said, and the list is growing.
“We are getting really good at picking out healthy embryos to implant,” Dr. Alan Copperman, director of the Division of Reproductive Endocrinology and Infertility at Mount Sinai Medical Center in New York and co-director of Reproductive Medicine Associates, told Healthline. “We are avoiding a lot of miscarriages and improving the health of the next generation.”
Choosing Sex, Eye and Hair Color?
Deciding whether or not to use genetic screening to select a healthy embryo is a straightforward decision.
“IVF and preimplantation screening spare a woman from getting pregnant with a fetus that has a genetic disease or a mutation that leads to dire illness,” said bioethicist Thomas Murray, Ph.D., senior research scholar and president emeritus of The Hastings Center. “The ethical case for not implanting this embryo is powerful. But then you get people who care about the sex of their child or want to select an eye color. The technology is not limited to finding and preventing horrible illness.”
Current technology does not allow parents to order up an embryo by sex, eye color, hair color, or other physical trait. But they can create embryo after embryo and choose which embryo to implant. If they try long enough and can afford it, they may be able to create and select an embryo that has the desired sex, eye color, and hair color.
“Human eyes are brown by default,” Steinberg explained. “A minor variant to a single gene can give you hazel eyes. Major variants give you blue eyes or green eyes. We can predict with great certainty the eye color your embryo will develop.”
Screening for hair color is still a question. David Kingsley, Ph.D., professor of Developmental Biology at Stanford University and researcher at the Howard Hughes Medical Institute, led a team that recently identified a blond hair gene in mice. Their study was published in Nature Genetics in June.
A Fix for Faulty Genes
In August, Dr. Yuet Kan, a professor of Medicine at the University of California, San Francisco School of Medicine, published a new technique to correct the faulty gene that causes thalassemia, a type of anemia that is one of the most common genetic diseases in the world. The study was published in Genome Research.
The gene-editing tool, called CRISPR/Cas9, let researchers cut out the faulty section of the gene responsible for thalassemia and replace it with the correct sequence. The result was healthy red blood cells in a lab dish. Kan didn’t transfuse the healthy blood cells back into the patient with thalassemia. That step would have taken more research and special approval from an ethical review board.
And then there is mitochondrial transfer.
Mitochondrial disease occurs when the mitochondria, tiny organs inside most of the cells in the body, fail to function properly. When an egg is fertilized, the mitochondria in the egg are passed on to the embryo. If genes in the mother’s mitochondria are faulty, the errors will be passed to the child.
Up to 4,000 children with mitochondrial diseases are born in the United States every year.
Most mitochondrial diseases are impossible to treat. The result can be loss of motor control, muscle weakness and pain, gastrointestinal problems, difficulty swallowing, poor growth, heart disease, liver disease, diabetes, respiratory problems, seizures, problems seeing and hearing, delayed development, and more.
What is the solution? Lose the bad mitochondria.
Using IVF, an egg from the woman with bad mitochondria is fertilized. So is an egg from another woman with healthy mitochondria. The nucleus, the part of the cell that contains the 46 chromosomes, is removed from the egg with the healthy mitochondria. The nucleus from the egg with the bad mitochondria is transferred to the first egg.
The result is an embryo with 23 chromosomes from the father, 23 chromosomes from one mother, and mitochondria from the other mother. The process works in animals but has not been tested in humans. Some believe it never should be.
Mitochondrial Transfer Is Controversial
“There have been a lot of dubious claims made about the science of mitochondrial transfer,” said Marcy Darnovsky, executive director of the Center for Genetics and Society (CGS), an advocacy group in Berkeley, California that opposes genetic manipulation in humans.
There is a bright line between screening technologies that identify genetic disorders and genetic manipulation that produces changes that will be inherited by the next generation, she told Healthline. PGD for thalassemia is appropriate because it prevents disease in the offspring. Mitochondrial transfer is inappropriate because the genetic changes will be passed on to future generations.
But what about gene repair to cure thalassemia, or PGD to select sex? Whether any of those practices are right, wrong, or even questionable, is up for debate. That debate has not happened.
“We need a robust public discussion of which technologies and practices are in keeping with women’s and babies’ health without moving down more dangerous roads,” Darnovsky said. “We need to treat these powerful technologies like we treat any other powerful technology. We need public discussion and we need public policy.”
But policy shouldn’t restrict scientific research, Murray said. The problem isn’t technology, but the uses to which it may be put. The question isn’t can we design babies for sex, eye color, and other traits parents want, but should we?
“We need to engage seriously about the limits of parental discretion when it comes to selecting traits for their children,” he said. “We haven’t had the conversation we need to have about this issue.”
Copperman offered a practical approach. If a particular reproductive technology makes you feel squeamish, stop and think. Parents shouldn’t use a technology that leaves them feeling uncomfortable. And reproductive medicine must clarify its own role.
“We need to take back the term ‘designer baby’ to mean designing the healthiest possible baby,” he said. “To talk about designing your baby the way you would design your next car is misleading. The technology to do that isn’t there today and it may never be there,” concluded Copperman.