For the first time, scientists have reversed an inherited disease from a human embryo using a revolutionary form of “chemical surgery” on the genetic code.
Researchers from Sun Yat-sen University in China corrected a faulty gene that causes a life-threatening blood disorder called beta-thalassemia using base-editor technology. While still very much in the early stages of development, the study shows how scientists might someday be able to cure a range of inherited diseases, such as sickle cell disease and cystic fibrosis.
Here’s how it works. DNA is made up of four bases known as adenine, cytosine, guanine, and thymine (or just A, C, G, and T). These four bases are essentially a code that living cells use as instructions to produce proteins. Beta-thalassemia is caused by a change to a single base, known as a “point mutation”, within the 3 billion bases of our genetic code.
As explained in the journal Protein and Cell, the researchers searched through this huge code to find the error and converted the G base to an A base, thereby ridding the embryo of the inherited disease. So far, this technique has proved to be over 23 percent effective in human embryos.
The technique was pioneered by Professor David Liu of Harvard University over the past few years. It’s comparable to other freshly developed gene-editing techniques like CRISPR-Cas9. CRISPR cuts strands of DNA at specific points using enzymes derived from bacteria and then inserts new genetic material. By contrast, this new base-editor technology chemically alters a single one of the DNA’s bases.
The experiment was carried out on a batch of lab-made embryos created from the skin cells of a patient with the condition. While the embryos were not used to produce babies, the experiment has raised some ethical questions about the future of gene-editing research and the use of human embryos.
The breakthrough has already been described by British scientists as “powerful”, “striking”, and “highly significant", however they admit there’s still much to consider and work on beyond the initial excitement.
“For many years, we have been saying that direct gene editing in embryos is some way in to the future. Now the future is here and there is much to consider,” Darren Griffin, Professor of Genetics from the University of Kent, said in a statement.
“While this is undoubtedly a highly significant advance, it is important not to get carried away about its widespread utility if put into clinical practice. An embryo would still need to be diagnosed as abnormal (if there were other embryos in the cohort that were normal they would presumably be used instead), then the base editor applied, then re-diagnosed to make sure that it had worked. This would be an involved procedure that would be very expensing,” he added.
“In the meantime, the ethical implications of gene manipulation in embryos need a thorough examination where safety is of paramount concern.”