A video shows the injection of gene-editing chemicals into a human egg near the moment of fertilization.
According to Oregon Health and Science University (OHSU), adjustment of genes in a human embryo has been used for the first time in the United States.
Although details are scarce at this point, sources familiar with the work assert that the research involved changing the DNA of one-cell embryos using CRISPR gene-editing.
The goal is to be able to correct defective genes that would cause inherited diseases. But further success with this kind of research is likely to raise the heated discussion on the ethical implications of genetically altering human embryos.
If the technique proves to be safe, such gene-edited embryos would develop into people who would no longer pass down their familial genetic afflictions to subsequent generations.
But many are opposed to these types of experiments, including religious, civil society and biotech groups. US Intelligence agencies have warned against CRISPR, calling it a potential "weapon of mass destruction".More news: Samsung Electronics reports 88.9 percent jump in Q2 net profit
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Scientists in China have attempted the same experiments on human embryos, to mixed results.
Dr. Robert C. Green, a medical geneticist at Harvard Medical School, said the prospect of editing embryos to avoid disease "is inevitable and exciting", and that "with proper controls in place, it's going to lead to huge advances in human health".
"So far as I know this will be the first study reported in the U.S.", said Jun Wu from the Salk Institute in the USA, who was involved in the project. One day, CRISPR could allow us to delete genes in order to eradicate genetic diseases, add in new genes in order to vastly improve various biological functions, or even genetically modify human embryos in order to create an entirely new class of humans...of super humans. That effect, called mosaicism, lent weight to arguments that germline editing would be an unsafe way to create a person.
Some countries have signed a pact to prohibit the practice for the reason that this could lead to the creation of so-called designer babies. Embryos at this stages are tiny clumps of cells invisible to the naked eye.
But the team behind the work has yet to publish its findings in a scientific journal, and peers said it was too early to judge how successful the results might be. They significantly reduced mosaicism.
That concept is similar to one tested in mice by Tony Perry of Bath University.
In this way, researchers can precisely turn off specific genes in the genome. In 2007, he unveiled the world's first cloned monkeys. But it is not clear what disease or genes were edited.