Science fiction is now barely a step away from reality, as cutting-edge biotechnology brings humanity before an unprecedented evolutionary and ethical crossroads. While pioneering gene therapies are already being deployed in hospitals to save lives from incurable diseases, patients still face the risk of passing these mutations on to future generations. The great taboo of science, germline editing (human germline modification), remains strictly prohibited in dozens of countries due to the incalculable risks posed by altering the DNA of embryos. The global community froze in 2018 when the "guilty" secret experiment of Chinese researcher He Jiankui was revealed; he had secretly proceeded with the birth of the first genetically modified children, sparking international outrage and leading to his immediate imprisonment. Today, however, two new studies from leading Western universities, Cambridge and Columbia, are changing the landscape. Using a revolutionary new precision technique, base editing, scientists have managed to correct the DNA of human embryos in the lab with unprecedented safety, drastically reducing the previously catastrophic chromosomal errors. Although these embryos were destroyed within the legal timeframe and were not used for pregnancy, this rapid progress reignites the worst fears of bioethicists. As technical barriers fall one after another, the nightmare scenario of a two-tier society, where access to DNA modification is a privilege of the few, looks increasingly visible, opening the door wide to the creation of a "genetic elite" and designer babies.
"Six years ago, I believed that using genome editing on human embryos was completely unfeasible," said Amander Clark, a professor of molecular cell and developmental biology at the University of California, Los Angeles (UCLA) and director of UCLA's Center for Reproductive Science, Health, and Education, who was not involved in the research. "This work restores the possibility that genome editing for therapeutic purposes could become feasible in in vitro fertilization (IVF) embryos in the future."
Laboratory research on human embryos, which are typically donated by patients undergoing IVF, remains strictly regulated in most countries and is usually permitted only for a period of 14 days after the embryo's creation. It is also unclear how supportive public opinion is toward genetically modified babies. Beyond issues of medical safety, skepticism is largely fueled by ethical questions surrounding the potential use of this cutting-edge technology to create so-called "designer babies", whose genes are deliberately altered or selected for desired traits.
Sharpening a "blunt" tool
The genome editing technique known as CRISPR-Cas9 is used in laboratories worldwide and has revolutionized scientific research, allowing scientists to edit the genes of living organisms for biotechnological and medical research. In 2020, two of the scientists who developed the technology won the Nobel Prize in Chemistry, and in 2023, the US Food and Drug Administration (FDA) approved the first two gene therapies for sickle cell disease—a debilitating and life-threatening inherited red blood cell disorder that disproportionately affects African Americans.
However, in some respects, CRISPR-Cas9 remains a blunt, unrefined tool. When this technology edits DNA, it causes a double-strand break in the helix at the target site. When used to modify human embryos, several studies have shown that it can lead to large and unintended changes—possibly even the loss of an entire chromosome.
The secret experiment of China
The possibility of unknown health impacts is one of the reasons why the scientific community condemned the work of Chinese researcher He Jiankui when he revealed in 2018 the existence of twin baby girls born from embryos he claimed to have modified using CRISPR-Cas9 to make them resistant to HIV. In 2019, he was sentenced to three years in prison, but has since been released. He did not respond to a request for comment.
Altering a single "letter" of DNA
A newer, more precise form of CRISPR, known as base editing, can change a single letter (or base) of DNA at a time. Base editing was first used in a clinical trial in 2022 to modify the immune cells of a teenager in the United Kingdom, after doctors had exhausted every other option to treat her leukemia. Since then, eight other children and two adults have received the therapy. Last year, doctors used base editing to treat a baby born with severe CPS1 deficiency, a rare and dangerous genetic disease.
Now, two new studies have used this technique to edit human embryos in the early stages of their development, which were donated for research purposes by individuals undergoing IVF treatment. Both teams found that the precision of the technique reduced the likelihood of unintended chromosomal abnormalities.
Kathy Niakan, professor of reproductive physiology and director of the Loke Centre for Trophoblast Research at the University of Cambridge, and her team used the technique to better understand how a pivotal gene functions in the development of the human embryo. They discovered that a gene called NANOG—named after the mythical Celtic Tír na nÓg, the land of eternal youth—plays a key role in how the first embryonic cells form that will eventually become the embryo and the placenta. The study was published on June 25 in the scientific journal Nature.
Niakan stated that base editing represents a significant advance over conventional CRISPR-Cas9 because it carries a much lower risk of causing unintended chromosomal errors. "Base editing can precisely alter a single nucleotide base pair in an entire human genome of approximately 3 billion base pairs—that is an incredible feat," she explained.
In a separate study, Dietrich Egli, associate professor of developmental cell biology at Columbia University, used base editing to introduce one of two genetic mutations into newly fertilized eggs. One targeted a gene known as PCSK9 which regulates cholesterol, and the other targeted HBG, which encodes the fetal form of hemoglobin, an oxygen-carrying protein. He chose these two genes because they were well-studied targets in non-heritable gene editing. Egli stated that a peer-reviewed scientific journal has accepted the study conditionally.
Ethical concerns and the "Gattaca syndrome"
Laurie Zoloth, professor of religion and ethics at the University of Chicago, stated that the research has once again reignited the ethical debate regarding the modification of human embryos. She noted that editing embryos carries many risks and, therefore, excluding its use in scientific research, it should remain prohibited for the time being, for safety reasons alone. She also pointed out that there are already ways to avoid the birth of children with genetic disorders—through pre-conception genetic screening, testing during pregnancy, and pre-implantation genetic testing during IVF.
"The problem of mosaicism has not been resolved; they do not really understand the long-term effects of the intervention; and there is no way to test a pregnancy without... an actual pregnancy and a child," she stated in an email. There are also long-term theological and philosophical issues surrounding "designing" babies with desirable traits, she added.
"These are even more profound when we appear to be designing babies who in the distant future would run a lower risk of cardiovascular problems—problems that could be addressed with lifestyle changes and that might well be fully treatable with drugs in that hypothetical future."
While embryo editing might be justified to prevent conditions like Tay-Sachs disease (a fatal neurological disorder manifesting in the first months of life), Zoloth warned that there will likely be a "slippage from therapy to genetic enhancement." This situation could lead to what she calls the "Gattaca problem," named after the 1997 film, which imagines a society obsessed with and determined by genetic perfection.
"Will this path lead us to an even more unjust future, where the children of the wealthy will be genetically 'curated', while the children of the poor, without resources, will be unable to compete in a democracy?" she wondered. "It is remarkable that, on the one hand, we may have the ability to spend so many resources and attention on altering the genetic code of an embryo to bring it exactly in line with what we consider normal or optimal, at a time when we cannot figure out how to provide clean, safe, and creative elementary schools with well-paid teachers for children after they are born," Zoloth added, noting that our knowledge of how human genetics influences physical traits and behavior remains very limited.
A recent survey regarding public attitudes toward human embryo research in four countries showed that the majority of respondents in the United Kingdom, the Netherlands, and Spain support the use of genome editing in embryos to help achieve a pregnancy by eliminating a serious or life-threatening condition. However, in Italy, this percentage was 46%.
Zoloth concluded by noting that while bioethicists have a duty to reflect and raise questions, a blanket ban on science also carries risks. "We do not want to ban scientific inquiry," she said. "That is why it is important to establish guardrails for the new science, protecting both the research itself and society."
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