For the first time ever, scientists have reported editing the genetic code in human embryos. The work, carried out by researchers in China, sought to remove a gene responsible for a potentially fatal blood disorder using embryos sourced from a local fertility clinic. Although the study purposely used a type of embryo incapable of developing into a live birth, scientists have warned about the ethical implications of the work. The technique used to edit the genetic material — known as CRISPR — is potentially capable of not only removing diseases from the human genome, but also enhancing traits such as intelligence and beauty.

scientists called for a global ban on editing the human genome in March

Nature News notes that rumors about the work, led by Junjiu Huang of Sun Yat-sen University in Guangzhou, have been circulating for a while in the scientific community. Scientists responded preemptively in March, calling for a temporary worldwide ban on the use of CRISPR to edit human genes until the implications had been better examined. In an article published in the journal Science, leading biologists warned about the dangers of altering the human germline (meaning permanent changes to the egg, sperm, or embryo that can be passed on to future generations). They note that the "enormous opportunities" of such genetic engineering come with "unknown risks to human health and well-being."

"It raises the most fundamental of issues about how we are going to view our humanity in the future and whether we are going to take the dramatic step of modifying our own germline and in a sense take control of our genetic destiny, which raises enormous peril for humanity," George Q. Daley, a stem cell expert and member of the group behind the Science paper told The New York Times last month. Daley and his colleagues noted that although a moratorium on human gene editing might be obeyed in the US and Europe, scientists in more "lax jurisdictions" might be tempted to experiment regardless of the ethical and clinical problems.

precise genetic engineering has been made possible by CRISPR — unveiled in 2012

Until quite recently, the prospect of creating heritable modified genes was a distant one. The theory of simply examining the genome and cutting out the genes responsible for specific diseases is straightforward enough, but researchers lacked a "knife" that was sharp and precise enough to carry out the work without missing their target. In 2012, such a tool arrived in the form of CRISPR — a technique that co-opts molecules used by bacteria to fight viruses, directing them to make precise cuts in genomes instead. The technique has already been used to modify genetic material in animals such as mice and monkeys, and now it is being turned to the human genome as well.

scientists face both practical and ethical challenges

However, as scientists warned in March, and as this recent research shows, we are still a long way from simply manufacturing babies that are more intelligent or more beautiful than their non-genetically modified peers. The study from China — published in the open access journal Protein & Cell after being rejected by Nature and Science for ethical reasons — used a total of 86 "non-viable" human embryos, but only 71 survived the process. Of these, only a fraction were actually found to accept the material intended to replace the genes causing the blood disorder, and even then, the genomes that were edited were a mix of changed and unchanged cells.

As Carl Zimmer notes in National Geographic, there were several major problems with the work, including the fact that the CRISPR technique often missed its target, inserting the DNA into the wrong place in the genome. "Such a misfire wouldn’t just fail to fix a disease," writes Zimmer. "It could create a disease of its own." He adds that despite this and other mistakes, there was nothing in the researchers' work that was a "conceptual deal-breaker" for using CRISPR to edit human genes. Future work and research will most likely improve upon the accuracy and efficiency of the technique. However, this will only lead to new and more profound difficulties.