WASHINGTON • Scientists have successfully edited the DNA of human embryos to erase a heritable heart condition that is known for causing sudden death in young competitive athletes, cracking open the door to a controversial new era in medicine.
This is the first time gene editing on human embryos has been conducted in the United States. Researchers said in interviews this week that they consider their work very basic. The embryos were allowed to grow for only a few days, and there was never any intention to implant them to create a pregnancy.
But they also acknowledged that they will continue to move forward with the science, with the ultimate goal of being able to "correct" disease-causing genes in embryos that will develop into babies.
News of the experiment began to circulate last week. Details became public on Wednesday with a paper in the journal Nature, triggering calls for a deeper debate on the ethics of altering the human genome.
The experiment is the latest example of how laboratory tool CRISPR (or clustered regularly interspaced short palindromic repeats), a type of "molecular scissors", is pushing the boundaries of humans' ability to manipulate life, and has caused excitement and horror. The study is especially sensitive as it involves changes to the germ line - genes that could be passed on to future generations.
A February report by the National Academies of Sciences, Engineering and Medicine urged caution in applying CRISPR to human germ-line editing, but laid out conditions by which research should continue. The new study abides by those guidelines.
Dr Shoukhrat Mitalipov, a lead author of the paper and a researcher at Oregon Health & Science University, said he is conscious of the need for a larger ethical and legal discussion, but that his team's work is justified as it involves "correcting" genes rather than changing them.
"Really, we didn't edit anything. Neither did we modify anything," Dr Mitalipov said. "Our programme is towards correcting mutant genes."
University of Wisconsin at Madison bioethicist Alta Charo, co-chair of the National Academies panel looking at gene editing, said: "What this represents is a fascinating, important and rather impressive incremental step towards learning how to edit embryos safely and precisely."
However, "this is not the dawn of the era of the designer baby", she added. She said some desired characteristics, like intelligence or athleticism, are influenced by multiple genes and researchers do not understand all components of how such features are inherited, much less have the ability to redesign them.
The research involved eggs from 12 healthy female donors and sperm from a male volunteer carrying the MYBPC3 gene, which causes hypertrophic cardiomyopathy. The disease causes an abnormal thickening of the heart muscle, and can lead to sudden cardiac death. There is no way to prevent or cure it, and it affects one in 500 people worldwide.
Around the time the sperm was injected into the eggs, researchers snipped out the gene causing the disease. The result: As the embryo's cells began to divide and multiply, a huge number appeared to repair themselves by using the normal, non-mutated copy of the gene from the women's genetic material.
Dr Mitalipov said he hoped the technique could one day be applied to a wide variety of genetic diseases.