New York, July 27: In a first in the US, scientists using the 'CRISPR' genome-editing technique, have successfully corrected the DNA in human embryos that carried inherited diseases.

The effort to create genetically modified human embryos was carried out by Shoukhrat Mitalipov from the Oregon Health and Science University and involved changing the DNA of a large number of one-cell embryos, MIT Technology Review reported.

"So far as I know, this will be the first study reported in the US," said Jun Wu, a collaborator at the Salk Institute in La Jolla, California, who played a role in the project.

Mitalipov declined to comment on the results which, he said, are pending publication.

In the process termed "germline engineering", the scientists demonstrated that it is possible to safely and efficiently eradicate or correct defective genes that cause inherited diseases like the blood condition beta-thalassemia.

As a result, any genetically modified child would then pass the changes on to subsequent generations via their own germ cells-the egg and sperm.

Until now, three previous reports of editing human embryos were published by scientists in China.

The earlier Chinese publications, although limited in scope, found 'CRISPR' caused editing errors and that the desired DNA changes were taken up not by all the cells of an embryo, only some.

That effect, called 'mosaicism', lent weight to arguments that 'germline editing' would be an unsafe way to create a person.

"But Mitalipov and his team are said to have convincingly shown that it is possible to avoid both mosaicism and 'off-target' effects, as the 'CRISPR' errors are known," the report noted.

According to a person familiar with the research, "many tens" of human IVF embryos were created for the experiment using the donated sperm of men carrying inherited disease mutations. The research, however, was limited to the lab and the embryos were not meant to be implanted into the womb.

"It is proof of principle that it can work. They significantly reduced mosaicism. I don't think it's the start of clinical trials yet, but it does take it further than anyone has before," a scientist familiar with the project was quoted as saying.

Mitalipov's group appears to have overcome earlier difficulties by "getting in early" and injecting CRISPR into the eggs at the same time they were fertilised with sperm.

However, some critics have opposed the 'germline experiments' as it could open the floodgates to a brave new world of 'designer babies' engineered with genetic enhancements-a prospect bitterly opposed by a range of religious organisations, civil society groups and biotech companies.

"Genome editing to enhance traits or abilities beyond ordinary health raises concerns about whether the benefits can outweigh the risks, and about fairness if available only to some people," said Alta Charo, Professor at University of Wisconsin-Madison.

US scientists correct DNA in lab-grown human embryos