CHICAGO (Reuters) - Top scientists and ethicists from seven countries on Wednesday called for a global moratorium on gene editing of human eggs, sperm or embryos that would result in genetically-altered babies after a rogue Chinese researcher last year announced the birth of the world’s first gene-edited twins.

FILE PHOTO: Scientist He Jiankui attends the International Summit on Human Genome Editing at the University of Hong Kong in Hong Kong, China November 28, 2018. REUTERS/Holly Chik/File Photo

News of their birth prompted global condemnation of the work, raising the ethical specter of so-called designer babies in which embryos could be genetically modified to produce children with desirable traits.

The scientists and ethicists want to halt genetic alterations of “germline cells” - egg or sperm cells - that can then be inherited by others and “could have permanent and possibly harmful effects on the species.”

The global moratorium would be in place until nations can devise international principles to guide how the technology should be used, the experts wrote in the journal Nature. It would not cover gene editing done in embryos for research purposes that would not lead to a live birth.

“The governance framework we are calling for will place major speed bumps in front of the most adventurous plans to re-engineer the human species,” the experts said in a commentary in the Nature. “The introduction of genetic modifications into future generations could have permanent and possibly harmful effects on the species,” they wrote.

Such work differs from research being conducted by numerous drug companies and scientists into gene therapies based on editing so-called somatic cells that affect an individual’s health by correcting a disease or condition but would not be passed on to offspring.

Dr. Francis Collins, director of the U.S. National Institutes of Health, said in a letter to the journal that the “NIH strongly agrees” that a ban on the practice should go into immediate effect and stay in place until nations can commit to international rules to determine “whether and under what conditions such research should ever proceed.”

“There is no doubt that genome editing technologies hold huge potential,” Collins said, but added that there are too many scientific and ethical questions that need to be answered.

Some scientists called the proposed ban unnecessary, saying it would not prevent a scientist bent on using the technology from editing DNA in embryos to prevent disease or enhance traits of a child, as was the case with Chinese researcher He Jiankui.

“We do not think a moratorium would have deterred He Jiankui, who acted secretively and in breach of a clear scientific consensus that germline genome editing should not be used in the clinic at this time,” Sarah Norcross, director of Britain-based Progress Educational Trust, said in a statement.

Helen O’Neill, program director for Reproductive Science and Women’s Health at University College London, said the proposal ignores the fact that a global ban already exists.

O’Neill said there were legal and ethical measures in place in China and that He broke many of these rules. “It was not that he did this because the law allowed it.”