In breakthrough, scientists edit a dangerous mutation from genes in human embryos

Scientists for the first time have successfully edited genes in human embryos to repair a common and serious disease-causing mutation, producing apparently healthy embryos.

But the achievement is also an example of human genetic engineering, once feared and unthinkable, and is sure to renew ethical concerns that some might try to design babies with certain traits, like greater intelligence or athleticism.

Scientists have long feared the unforeseen medical consequences of making inherited changes to human DNA. The cultural implications may be just as disturbing: Some experts have warned that unregulated genetic engineering may lead to a new form of eugenics, in which people with means pay to have children with enhanced traits even as those with disabilities are devalued.

“We’ve always said in the past gene editing shouldn’t be done, mostly because it couldn’t be done safely,” said Richard Hynes, a cancer researcher at the Massachusetts Institute of Technology. “That’s still true, but now it looks like it’s going to be done safely soon,” he said, adding that the research is “a big breakthrough.”

Scientists at Oregon Health and Science University, with colleagues in California, China and South Korea, reported that they repaired dozens of embryos, fixing a mutation that causes a common heart condition that can lead to sudden death later in life.

If embryos with the repaired mutation were allowed to develop into babies, they would not only be disease-free but also would not transmit the disease to descendants.

The researchers avert two important safety problems: They produced embryos in which all cells — not just some — were mutation-free, and they avoided creating unwanted extra mutations.

Much more research is needed before the method could be tested in clinical trials, currently impermissible under federal law. But if the technique is found to work safely with this and other mutations, it might help some couples who could not otherwise have healthy children.

The researchers also discovered something unexpected: a previously unknown way that embryos repair themselves.

In other cells in the body, the editing process is carried out by genes that copy a DNA template introduced by scientists. In these embryos, the sperm cell’s mutant gene ignored that template and instead copied the healthy DNA sequence from the egg cell.

And some embryos had cells that did not get repaired — a phenomenon called mosaicism that could result in the mutation being passed on — as well as unplanned mutations that could cause other health problems.

In February, a National Academy of Sciences, Engineering and Medicine committee endorsed modifying embryos, but only to correct mutations that cause “a serious disease or condition” and when no “reasonable alternatives” exist.

Sheldon Krimsky, a bioethicist at Tufts University, said the main uncertainty about the new technique was whether “reasonable alternatives” to gene editing already exist.

As the authors themselves noted, many couples use pre-implantation genetic diagnosis to screen embryos at fertility clinics, allowing only healthy ones to be 

implanted. For these parents, gene editing could help by repairing mutant embryos so that more disease-free embryos would be available for implantation.

The larger issue is so-called germline engineering, which refers to changes made to embryo that are inheritable.

“If you’re in one camp, it’s a horror to be avoided, and if you’re in the other camp, it’s desirable,” Dr. Greely said. “That’s going to continue to be the fight, whether it’s a feature or a bug.”

For now, the fight is theoretical. Congress has barred the Food and Drug Administration from considering clinical trials involving germline engineering. 

The authors say they hope that once the method is optimized and studied with other mutations, officials in the United States or another country will allow regulated clinical trials.

Adapted from: https://www.nytimes.com/2017/08/02/science/gene-editing-human-embryos.html?emc=eta1. Acesso em out. 2017.