Precise "chemical surgery" has been performed on human embryos to remove disease in a world first, Chinese researchers have told the BBC.
The team at Sun Yat-sen University used a technique called base editing to correct a single error out of the three billion "letters" of our genetic code.
They altered lab-made embryos to remove the disease beta-thalassemia. The embryos were not implanted.
The team says the approach may one day treat a range of inherited diseases.
Base editing alters the fundamental building blocks of DNA: the four bases adenine, cytosine, guanine and thymine.
They are commonly known by their respective letters, A, C, G and T.
All the instructions for building and running the human body are encoded in combinations of those four bases.
The potentially life-threatening blood disorder beta-thalassemia is caused by a change to a single base in the genetic code - known as a point mutation.
The team in China edited it back.
They scanned DNA for the error then converted a G to an A, correcting the fault.
Junjiu Huang, one of the researchers, told...