Scientists in the US have used CRISPR, a gene editing tool, to alter human embryos for the first time. During the trial, they used the technology to correct a genetic mutation that'd normally result in a heart defect. The test was carried out successfully by Shoukhrat Mitalipov, et al at Oregon Health and Science University.
Compared to the results in some of the international trials using human embryos, the embryos did better in this test. The scientists showed they could use CRISPR accurately and without causing any off-target mutations.
In some other tests, such as in China, off-target mutations have been an issue, raising safety concerns.