Genetic modification of embryos: The truth behind the research

Nearly two decades ago, in an attempt to increase funding for research on embryonic stem cells, scientists and patient-advocacy groups enlisted patients suffering from a range of debilitating diseases, from Alzheimer’s to multiple sclerosis. Promising the possibility of a “cure” if only we would embrace embryo-destructive research, we were told that compassion for suffering individuals demands that we prioritize science over misguided moral concerns about the embryo.

Fast forward nearly 20 years, and no embryonic stem cell-based treatments have yet reached the clinic. Despite this track record, the same scientific associations that oversold embryonic stem cells are now championing a new form of embryo-destructive research—the genetic modification of human embryos—as a method that will potentially cure a variety of genetic disorders. The reality, though, is that this embryo-destructive research will have virtually no utility in treating or preventing disease. Once again, we are being told to allow this research to progress under false pretenses and with potentially disastrous consequences. While it will never be used to cure disease, if this research is allowed to progress, it will be used for the genetic enhancement of humans.

The ability to edit a genome, i.e., insert or delete genetic material, is nothing new. Researchers have been doing this for decades with model research organisms such as fruit flies and mice. However, the techniques that have been used traditionally for such research did not readily lend themselves to the modification of human embryos.

The current push to do research on the genetic modification of human embryos stems from the recent development of the CRISPR/Cas genetic modification system. This technique, which has received a lot of media attention, allows genetic modifications to be done relatively cheaply in human cells with a higher level of precision and control. In fact, this technique is so robust that it has the potential to be used for making precise targeted modifications of the human germline.

Theoretically, this technique could be used for removing a defective copy of a gene in a human embryo and replacing it with an undamaged copy. It also could be used to insert genes associated with desired traits such as muscle strength or intelligence. While these are all possibilities, researchers are not quite there yet when it comes to doing this efficiently in human embryos.

Currently, there are three main technical hurdles associated with this technique. The first has to do with how well the process targets a specific site in the genome. While the process involves using a guide sequence to target the site in the genome the researchers are trying to modify, the guide can sometimes target other regions and create new mutations elsewhere in the genome. The second issue is that even if the guide sequence targets the proper site, the process can actually introduce mutations at this site rather than correct the damaged gene as intended. The third issue is mosaicism, in which the embryos are only partially altered such that some cells in the embryo still contain the mutated gene while other cells have a healthy repaired copy.

One of the first published studies examining the efficacy of using the CRISPR technique in human embryos focused on modifying the beta-globin (HBB) gene. The researchers found that very few of the embryos, less than 10 percent, had the HBB gene altered properly and that new mutations were created elsewhere in the genome, so called off-site mutations. In addition, they found that a significant number of embryos were mosaic in nature.

More recent studies though have shown more promising results; a higher efficacy in replacing the defective gene with no clear evidence of off-site mutations. However, mosaic embryos were still a problem in these studies. Most recently, researchers from the Oregon Health and Science University (OHSU) published a paper claiming close to 50 percent efficacy in repairing a damaged gene with no off-site mutations and no evidence of mosaic embryos.

While significant technical concerns still exist, one thing is clear from the trajectory of these studies; the research is progressing toward its possible clinical use. While there remains a ban on using federal funds to review or do this type of research given that it involves the deliberate destruction of human embryos, there is no outright ban in the US, as evidenced by the OHSA study. In fact, despite the federal funding ban, the National Academy of Sciences (NAS) issued a report supporting the pursuit of this research.

Specifically, the 2017 report advocated moving forward with research to remove defective genes associated with disease in human embryos. While the report tried to draw a line in the sand by stating that the technique should not be used for genetic enhancement, that is largely a distinction without a difference given the known difficulty of determining what is a defect and what is an enhancement. The reality is that if the technique for correcting “defective” genes becomes efficient and safe enough to reach the clinic, it will be nearly impossible to keep the technique from being used for “enhancement” given the difficulties of even defining what this actually entails.

The biggest issue with the NAS report, however, is that it its disingenuous in its advocacy. While the authors justify their support for this research in terms of curing diseases, the technique will have little to no utility in repairing defective genes in the clinic, a fact that is deliberately ignored by the academics who authored the report. While the NAS report claims that “in some situations, heritable genome editing would provide the only or the most acceptable option for parents who desire to have genetically related children while minimizing the risk of serious disease or disability” it is actually quite difficult to identify such a situation in practice.

Imagine the case where a husband and wife each carry a defective version of the HBB gene. This is normally a recessive defect such that the embryo would need two copies of the defective HBB gene in order to develop beta thalassemia, the blood disorder associated with this mutation. If the couple undergoes IVF to produce a number of embryos, only 25 percent of the embryos will have two copies of the defective gene. Pre-implantation genetic diagnosis (PGD), in which cells from the embryo are genetically screened, would allow for clinicians to select one of the 75 percent of embryos that lack the disease. One could even identify one of the 25 percent of embryos that completely lack a defective HBB gene.

Setting aside the significant ethical issues associated with PGD, no scientist or clinician would recommend trying to attempt the genetic modification of an embryo containing two copies of the defective HBB gene when healthy IVF embryos for the couple can be easily produced.

Even in the rare case that a husband and wife both have the same dominant genetic disorder, 25 percent of the embryos would still be healthy. It is only in the extremely rare case in which a husband and wife have the same recessive disorder (each has two defective copies of the gene in question), where PGD could not be done. Some have argued that it may have utility in cases where the couple has multiple genetic disorders that the child might inherit. However, screening multiple embryos is still likely to be much more efficient and cost-effective than correcting multiple genes in these embryos and then screening them to ensure the proper modifications had been introduced.

Rather than highlighting this, the NAS report skirts the issue acknowledging that “germline genome editing is unlikely to be used often enough in the foreseeable future to have a significant effect on the prevalence of these diseases,” but then arguing that it “could provide some families with their best or most acceptable option for averting disease transmission.” However, it fails to make clear how rare—virtually nonexistent—these cases actually would be.

Yet despite this fact, the research community, through embryo-destructive research, is intent on developing a radical new manner of “therapy” that promises little to no health benefit for those who suffer from disease. What it does promise—assuming the technical difficulties are overcome—is a procedure that will allow for the radical alteration of the human genetic program, and a further devaluation of human life.

As John Paul II wrote in Evangelium Vitae, research on human embryos, even under the pretext of medical progress “reduces human life to the level of simple ‘biological material’ to be freely disposed of.” In this manner, human life becomes a commodity that can be bought, sold, marketed, and shaped to the demands of an increasingly secular society. Already the widespread use of IVF fuels the belief that children are a “right” rather than a gift. The ability to genetically modify one’s children will only further contribute to this consumer mentality and, as John Paull II has said, a “civilization in which persons are used in the same way as things are used.” Is it any wonder that in such a society, the levels of childhood abuse continue to rise? Without the ability to see human life as a gift freely given, as having inherent, God-given dignity irrespective of our genetic make-up, we lose sight not only of what it is to be human but also of our ability to act humanely.