State of the ART

Emerging genetic technologies in reproductive medicine are rapidly making real what once was science fiction—are we ready for it?

In 1997, a science fiction film titled Gattaca premiered in U.S. theaters, depicting a society sometime in the not-so-distant future in which people are crafted for and judged by the quality of their genetic material. Unhealthy genetic predispositions to conditions such as heart disease and mood disorders are neatly avoided through the careful selection and manipulation of embryos well before pregnancy. “I have taken the liberty of eradicating any potentially prejudicial conditions,” explains a genetic counselor to a couple onscreen. “Premature baldness, myopia, alcoholism and addictive susceptibility, propensity for violence, obesity, etcetera.” Those born without the benefit of such interventions become the dregs of society—weaker, sicker, and never quite as successful.

This scenario would likely never happen in real life. Except here’s the catch—fertility specialists are already selecting embryos against cancers as well as genetic and neurological diseases. They’re on the brink of being able to analyze an embryo’s whole genome, while the technology that would enable precise manipulation of that same genome not only exists but has worked beautifully in monkeys. Right now, in the United States and the United Kingdom, certain forms of germline modification to human embryos are not only on the regulatory table but looked on with an apparent degree of favor.

The day may no longer be so far away when it won’t be technology or biology that will hold reproductive medicine back from this sort of future but simply science’s still-nascent understanding of genetics. This is forcing a new urgency on long-debated dilemmas in reproductive medicine about who should be born and with what advantages or disadvantages. Indeed, as one panelist said at a 2011 gathering of leading embryo genetics pioneers [1], “As far as I am concerned, Gattaca is here.”

Selecting for the Best

The backbone of reproductive medicine is a process called in vitro fertilization (IVF), in which eggs are taken from a prospective mother’s fallopian tubes, fertilized in a dish with the father’s sperm, and then, three to six days later, transferred to the mother’s body to become a fetus. The first IVF procedure took place 37 years ago and has since then helped more than 5 million babies come into being.

Genetic testing became a part of this process around 1990 when doctors began to screen embryos to avoid transferring ones that carried specific genetic diseases, such as cystic fibrosis or hemophilia. In short order, they also began screening more generally for chromosomal abnormalities to identify and transplant embryos free of abnormalities in their chromosomes—thus more likely to implant successfully in the uterus—a procedure that became and remains the primary reason for preimplantation genetic analysis.

Two techniques dominated in those early days: polymerase chain reaction (PCR) for specific genetic diagnoses and fluorescence in situ hybridization (FISH) for chromosome screening. However, FISH in particular, though widely used, was prone to error and misdiagnoses. This was partly because it relied heavily on single-cell biopsies of three-day-old embryos—a barely adequate and notoriously unreliable way to sample DNA—and also partly because the test itself was often hard to interpret and could never analyze more than about half of the 23 chromosomes available anyway.

But in the last half decade, more sophisticated analytics have emerged that counter many of these issues, such as single nucleotide polymorphism (SNP) arrays, array comparative genomic hybridization (aCGH), and quantitative PCR (qPCR). By and large, none of these stands out in particular from the others. All three comprehensively scan the entire chromosome and can pick up many more details than FISH. All three also have the advantage of safer and more reliable biopsy techniques like the trophectoderm biopsy, which samples more cells from the outer portion of a five- or six-day-old embryo. qPCR is the least robust, but also the most rapid, with a six hour or fewer turnaround time. aCGH provides more information but can also be performed relatively rapidly—within 12 hours—meaning that, in either test, the blastocysts could be assessed and transferred immediately rather than frozen while the analyses are completed. (Although cryopreservation has improved to such an extent that freezing is no longer a major risk and may even allow better results.) SNP arrays take the longest to complete but give back thousands of results per chromosome versus aCGH’s hundreds and can even trace specific defects back to the parent who passed them down.

The game changer in this area will be next-generation sequencing (NGS), and it’s coming quickly. The core idea here entails breaking DNA up into hundreds of thousands of fragments, sequencing them en masse in parallel reactions, and then reassembling them. It’s an extremely efficient technique, and for the time it takes, it provides far more data than aCGH and even SNP arrays, at a comparable price.

Early work in this area appeared last year in a 2014 report by a team led out of the University of Oxford, United Kingdom [2]. In their research, they validated an NGS protocol for embryo screening capable of the simultaneous analysis of chromosomal state, mitochondrial DNA, potentially even specific genetic disease mutations for up to 32 different samples with a 15-hour turnaround time and, thanks to the combined sequencing, two-thirds the price of existing sequencers. Following validation experiments, the team used the technique to identify healthy embryos for two couples, transferring back one apiece; both children were born in the summer of 2013, healthy and chromosomally identical to the NGS predictions.

The demand for chromosome screening and disease diagnostics is on the rise—the Oxford team has seen referrals for these services climb by more than 50% in the last two years, and other clinics are seeing similar numbers. The sheer price and convenience of tools such as NGS will only encourage this trend by making such tests cheaper and more accessible.

More testing is transformative in and of itself, but more than that, NGS will amplify the amount of information coming in to couples about their potential children. With diagnostics and screening in one test, couples looking to avoid a specific disease will be able to also scan for chromosomal health, and someday the reverse may become possible for couples ostensibly scanning for just chromosomal normality.

Eventually, as NGS analyses continue to become cheaper and easier, whole genome sequencing will enter into the process and provide more information across the board. Indeed, the Oxford authors had the ability to do a whole genome sequence on the embryos they tested. They simply chose not to.

Improving on the Best

Since 2011, the U.K. government has considered regulating techniques for a process called mitochondria replacement in its fertility clinics. Mitochondria are organelles within human cells that are crucial to energy regulation and production. They’re passed down from mother to child and carry their own DNA separate from the nucleus. Diseases stemming from mutations in this DNA are rare but potentially devastating and difficult to predict or screen for.

Two techniques now exist to eliminate the problem of defective mitochondria in women while still allowing them genetically related children of their own by swapping out the defective organelles for healthy ones. In pronuclear transfer, two eggs are fertilized: the prospective mother’s, with its mutated mitochondria, and a donor’s. The genetic information from the embryo made from the mother’s egg is plucked out and deposited into the donor embryo with its healthy mitochondria. Maternal spindle transfer, meanwhile, takes the DNA from the afflicted mother’s egg, transfers them into the donor egg, and then fertilizes the resulting single egg. The result in either case is an embryo with DNA from three people—the nuclear genes from the mother and father, and 37 mitochondrial genes from the donor— all of which are passed on through that child’s genetic line from that point forward.

The Human Fertilisation and Embryology Authority (HFEA), which is the U.K.’s governing body over reproductive medicine, has produced three reports in three years for its government, ultimately concluding that there is no evidence so far that mitochondrial replacement is unsafe, but that there is still a need for further research. In response, the U.K. government has submitted draft regulations for these techniques in clinics and sought public feedback; it’s expected to soon submit revised regulations to Parliament for a vote. The U.S. Food and Drug Administration (FDA) is second in line in this area, having held similar hearings on the subject in February 2014. If either of these efforts meets approval, it will mark the first sanctioned human germline modification in the world, breaking a longstanding global consensus against human genetic modification.

Even with high-powered selection techniques, such as NGS and SNP arrays, genetic selection will only ever help parents and clinicians choose among available embryos. If all of the options are defective, with broken chromosomes, defective mitochondria, or genetic carriers of future diseases, well, that’s the luck of the draw. But if techniques such as mitochondrial replacement are made available, some couples, at least those carrying that specific type of mitochondrial genetic defect, would be able to actively change their biological lot.

It may not have to stop with mitochondria either. In just the last two years, a breakthrough genome editing technology called CRISPR (short for Clustered Regularly Interspaced Short Palindromic Repeats) has already revolutionized molecular biology and genetics. Derived from a bacterial self-defense system, it allows fantastically efficient, easy, and precise gene editing for very little cost. Its immediate applications are in gene therapy and creating more accurate, less expensive animal models; however, its longer-term potential could easily encompass reproductive medicine if society allowed. In February 2014, a report in Cell from a Chinese research team announced the birth of healthy twin macaque monkeys born with multiple targeted genetic modifications made using CRISPR during the one-cell stage of IVF [3].

Jennifer Doudna at UC Berkeley led one of the teams that discovered CRISPR’s potential for fast and easy genome editing. Technologically speaking, she says the tool could be applied in humans today, although ethically, she points out, whether it should be applied is a different question. (Photo ­courtesy of Jennifer Doudna, UC Berkeley.)

Jennifer Doudna at UC Berkeley led one of the teams that discovered CRISPR’s potential for fast and easy genome editing. Technologically speaking, she says the tool could be applied in humans today, although ethically, she points out, whether it should be applied is a different question. (Photo ­courtesy of Jennifer Doudna, UC Berkeley.)

“The technology as it is today is capable of that kind of change in human embryos,” says Jennifer Doudna, a biochemist at the University of California (UC) at Berkeley who led one of the research teams that originally discovered CRISPR’s potential. “That really came home to everyone when the paper was published with the monkeys.”

Much work remains before it could safely be used in humans, Doudna hastens to point out. For instance, in studies with mice, some CRISPR manipulations have caused unintended off-target effects. The Chinese team analyzed the macaques’ genomes in search of similar effects and didn’t find any, but it’s still not clear yet why off-target effects happen, when they do occur, and how to stop them, and that’s something that would have to be fully worked out before CRISPR ever went into humans.

An illustration of the novel genetic editing tool CRISPR at work. Emerging genetic technologies will pose difficult ethical dilemmas for reproductive specialists and embryologists. (Image courtesy of Jennifer Doudna, UC

An illustration of the novel genetic editing tool CRISPR at work. Emerging genetic technologies will pose difficult ethical dilemmas for reproductive specialists and embryologists. (Image courtesy of Jennifer Doudna, UC

“But is it going to get there? No question,” Doudna says. “And that’s both an amazing thing and also a bit scary. It’s really a very, very powerful technology, and so I think the challenges are that you could ask well, if we can do this, why not do it?”

Do We Know What’s Best?

So, what happens when parents and a doctor can sequence the entire genome of their prospective children? What happens when the power to easily change that genome exists? Right now, not that much. Science’s ability to pick up on genetic differences has far outpaced its ability to make sense of that information. We know some specifics—the genetic variants that code for hemophilia and Huntington disease, for instance. We’ve identified genes associated with various conditions such as diabetes, mood disorders, and cancers, but these don’t account for the entirety of those disorders, and we’re still figuring out how they interact with each other and the environment to cause disease. Then there’s the fact that, in any given genome, there are countless variations that scientists can detect that no one knows what to make of yet. But we are learning, and the day may come when do know more of these answers—and that, says Josephine Johnston, a bioethicist and director of research at the Hastings Center, is when the questions really get tough.

“I think we are moving toward a position where we are giving people more and more information with which to decide who should be born,” says Johnston, “and we really do need to start talking about what that means and what kind of an obligation people have to each other and to future children, and to themselves in terms of how they use those technologies.”

A 2008 survey of assisted reproductive technology (ART) clinics in the United States found that, of the 137 responders who offered preimplantation genetic screening, the two most common reasons to use the service were to check for chromosomal abnormalities and for the presence of single-gene early-onset disorders, the two reasons the test was initially devised. However, in that same survey, 42% of clinics also indicated that they offered testing to select a child’s gender without a medical reason, and 24% were wiling to test for key immune genes to ensure that the child could serve as a source of stem cells for someone else with a disease such as leukemia (tissue typing). These aren’t hypotheticals—they’re happening now. In fact, 3% of clinics in the survey even offer genetic testing to select for disabilities such as dwarfism or deafness.

“That’s a tough one,” says Bonnie Steinbock, a bioethicist and professor emeritus of philosophy at the University of Albany in New York. She describes a high-profile instance in the early 2000s, in which a lesbian couple in the United States, both deaf, wanted to ensure the deafness of their child. Clinics turned them away, but ultimately, the pair was able to find a deaf sperm donor for artificial insemination and their resulting son is mostly deaf. “Unlike other disabling conditions—and I do think that deafness is a disability—you have a community, a language, a culture. If these two women felt that they would be better parents to a deaf child, I don’t think that’s something that’s just terrible and has no validity,” she says. “On the other hand, children can be bilingual, so why not have a child who would be bilingual in hearing?”

The more we learn, the more complicated this gets. Right now, a number of clinics in the United States and Europe also screen for adult-onset conditions, such as early-onset Alzheimer’s and Huntington disease, but society hasn’t drawn a clear line delineating which diseases warrant passing an embryo up and which do not. Charles Coddington, a reproductive endocrinologist at the Mayo Clinic in Rochester, Minnesota, offers this example: imagine a couple with a genetic predisposition for a form of intestinal cancer that reliably manifests in a carrier’s 50s. “This is terrible,” he says, “but by age 55, you can live a healthy, good life otherwise—do we want to throw away that embryo?”

In 2012, Spain reported its first clinical case of preimplantation genetic diagnosis for the BRCA1 mutation associated with an increased risk of breast cancer. Did that heightened risk justify discarding the carrier embryos? What if that embryo was one of those carriers that would not go on to develop cancer? In that vein, several specific genetic changes have recently been associated with diseases such as schizophrenia, major depression, and attention deficit hyperactivity disorder. Would these predispositions qualify a given embryo as too flawed to exist? If not, would parents actually have a moral obligation to test for them? And since there is no such thing as a genetically perfect person or embryo, that means that tradeoffs will almost certainly need to be made—what’s better for your child’s future: diabetes or depression?

All the Best Intentions

These are the kinds of questions that the bioethics literature has kicked around for decades. Only now, not only are they less philosophical but new angles are appearing quickly thanks to newer techniques such as CRISPR, mitochondrial replacement, and even lab-made gametes—a similarly revolutionary fertility technology under development in stem-cell circles (see Leslie Mertz’s article on page 16 of this issue of IEEE Pulse). For instance, is it theoretically more ethical to manipulate an embryo’s genome to solve health dilemmas rather than discard it outright? Just pluck that pesky BRCA1 mutation out of an otherwise stellar embryo and forget about whether the person would or wouldn’t have had cancer down the line? Granted, the idea strays deeply into Gattaca territory, but does that make it morally wrong?

“What is so special about the human genome?” asks Simon Fishel, managing director of the CARE Fertility clinics network in the United Kingdom and an IVF pioneer. He points to diabetics and their daily insulin injections. “If you get to the point where we can understand that and manipulate for good before waiting to see the pain and suffering and try to correct it later, then you could change the life of that individual from the moment of its birth, rather than having to live with it for the rest of its life an inadequate therapy,” he argues. “That has to be a positive.”

It’s an argument that gains added momentum in the face of the mitochondrial replacement work already on the table. As an editor’s comment in the journal Reproductive Biomedicine Online pointed out [4], some mitochondrial diseases actually stem from nuclear mutations, not mitochondrial ones, and if the consensus against germline engineering can be broken for one subset of mitochondrially impaired patients, why not the others? And if the rules are bent for that population…

This is the classic slippery slope argument that has always haunted assisted reproduction. Scientists don’t know the whole complement of genes that result in intelligence, but as of a 2014 report from the Stanford University School of Medicine, they do know a key gene for blond hair [5]. What’s to stop parents and clinicians from going past diabetes and into aesthetics? In 2009, a fertility clinic with offices in California and New York announced that it would soon allow couples to screen and select embryos for not just gender but also for hair, skin, and eye color. “This is cosmetic medicine,” the clinic’s director Jeffrey Steinberg told The Wall Street Journal at the time. “Others are frightened by the criticism, but we have no problems with it.”

Regulations exist around the world moderating the extent of testing and other practices, but these are patchwork. The United Kingdom’s HFEA is a particularly well-established governing body for reproductive care, acting to monitor and license fertility clinics and embryo research, maintain registries on outcomes and practices, and provide specific guidance on what can and cannot be done. Among other regulations, the HFEA allows analyses for chromosomal assessment, approved genetic disorders, and tissue typing but not nonmedical sex selection and certainly not for cosmetic traits. No mitochondrial replacement work can be performed yet. Clinics that do not comply with the HFEA regulations can be warned, sanctioned, or even have their license revoked or suspended.

On the other hand, the United States is less formally regulated. The federal government, via the usual processes of the FDA, approves relevant drugs, devices, and biologics and has claimed mitochondrial replacement techniques as subject to its authority. The U.S. Centers for Disease Control and Prevention (CDC) also maintains a voluntary database of clinical practices and success rates; however, there are no binding rules on practices such as embryo transfer or genetic scanning—not even against scanning for nonmedical genetic traits. The American Society for Reproductive Medicine and the Society for Assisted Reproductive Technologies provide recommendations similar to those of the HFEA (although they do not prohibit nonmedical gender selection), but they have no teeth with which to enforce these guidelines short of peer pressure and the expulsion of nonadherents (who can still continue to practice). Around 10–12% of operating U.S. fertility clinics do not comply with requirements to report their practices and success rates to the CDC.

Steinberg eventually did withdraw his offer for cosmetically selected babies, not because of any regulations or legality but because of the public and scientific outcry that erupted following his pronouncement. And that, in the end, may be the most important limit to all of these technologies. For reproductive medicine to slide into some sort of Gattacan reality, it will ultimately need the consent of society.

Petra de Sutter, who heads the Department of Reproductive Medicine at the Ghent University Hospital in Belgium, points to cloning as an illustration. Once the capacity to clone humans arose, experiments kicked off before any real dialogue had taken place with the general populace. A backlash ensued, and the brakes were hit hard and fast on the research. “This was a good example of how to not proceed,” de Sutter says. She urges scientists developing new reproductive technologies to discuss their work and its implications. “We should talk together with society at large from the beginning to know the direction we should take with our research. Scientists should not stay in their lab doing things and say, well we’ve done this and now from now on this is possible.”

And fortunately, these discussions are exactly what’s happening now. During its research into mitochondrial replacement, the HFEA in Britain also investigated public sentiment using polls, focus groups, face-to-face interviews, and public meetings; at Berkeley, Doudna is actively bringing scientists, lawyers, ethicists, and media together to discuss CRISPR and its ethical potential in genomics and public health. De Sutter herself has helped promote similar discussions with lab-derived gametes at Ghent University.

The huge majority of specialists in ART have no interest in bringing about designer babies—only healthy babies. The technical power to do this may become more complicated and invasive, but that doesn’t automatically mean that it has to be used. People might want to, yes—the HFEA found that the U.K. public generally supported mitochondrial replacement as long as it was proven safe and carefully regulated—but people might not want to edit out cancer genes. “And if society decides we don’t want it, that’s fine, then we don’t do it,” says de Sutter. The most important thing, she says, is to talk about it. “This research cannot stand alone.”

References

  1. K. Hens, W. J. Dondorp, J. P. M. Geraedts, and G. M. de Wert, “Comprehensive embryo testing. Experts’ opinions regarding future directions: An expert panel study on comprehensive embryo testing,” Hum. Reprod., vol. 28, no. 5, pp. 1418–1425, 2013.
  2. D. Wells, K. Kaur, J. Grifo, M. Glassner, J. C. Taylor, E. Fragouli, and S. Munne, “Clinical utilisation of a rapid low-pass whole genome sequencing technique for the diagnosis of aneuploidy in human embryos prior to implantation,” J. Med. Genet., vol. 51, pp. 553–562, 2014.
  3. Y. Niu, B. Shen, Y. Cui, Y. Chen, J. Wang, L. Wang, Y. Kang, X. Zhao, W. Si, W. Li, A. P. Xiang, J. Zhou, X. Guo, Y. Bi, C. Si, B. Hu, G. Dong, H. Wang, Z. Zhou, T. Li, T. Tan, X. Pu, F. Wang, S. Ji, Q. Zhou, X. Huang, W. Ji, and J. Sha, “Generation of gene-modified Cynomolgus Monkey via Cas9/RNA-mediated gene targeting in one-cell embryos,” Cell, vol. 156, no. 4, pp. 836–843, 2014.
  4. C. C. Wong and M. H. Johnson, “Therapy for mitochondrial genetic disease: Are we at the thin end of the wedge?” Reprod. BioMed., vol. 29, pp. 147–149, 2014.
  5. C. A. Guenther, B. Tasic, L. Luo, M. A. Bedell, and D. M. Kingsley, “A molecular basis for classic blond hair color in Europeans,” Nat. Genetics, vol. 46, pp. 748–752, 2014.