Chinese scientists have edited the genomes of human embryos for the first time, confirming a storm of rumors and igniting an ethical debate.

Researchers at Sun Yat-sen University in Guangzhou, China, used an experimental gene-editing technique to modify a gene in human embryos that causes a fatal blood disorder. The procedure, which was done in nonviable embryos, was only partially successful, Nature News reported.

The study, which was published online Monday (April 18) in the journal Protein & Cell, has raised questions in the scientific community over the risks of the procedure and the ethics of its use in humans. [Unraveling the Human Genome: 6 Molecular Milestones]

"Their study should be a stern warning to any practitioner who thinks the technology is ready for testing to eradicate disease genes," George Daley, a stem-cell biologist at Harvard Medical School in Boston, told Nature News.

The technique involves an enzyme complex known as CRISPR/Cas9, found in many bacteria. CRISPR (short for "clustered regularly interspaced short palindromic repeats"), is a short, repeated sequence of RNA that matches the genetic sequence the researcher wants to modify. It works in concert with Cas9, an enzyme that cuts DNA like a pair of molecular scissors.v