CRISPR Gene Editing Successfully Stops Muscular Dystrophy In Living Mice

If used on humans, the treatment could save hundreds of lives per year
Jennifer Doudna/UC Berkeley

Hundreds of children per year are born with Duchenne muscular dystrophy (DMD), a genetic disorder that leads to muscle weakness and atrophy—those numbers make it the most common fatal genetic disorder. Better care for the heart and lungs has extended the average lifespan of a patient with DMD to 27, but there is still no known cure for the disease. By harnessing the power of gene editing enzyme complex CRISPR, several teams of researchers have been able to tweak the genes of mice with the condition in order to treat it. A trio of studies, each with nearly identical experiments, was published last week in the journal Science.

People with Duchenne muscular dystrophy don’t produce a protein called dystrophin that keeps muscles from breaking down. That’s because they have mutations on a gene in the X chromosome that provides the blueprint for the protein. The genetic errors can look a little different—some people are missing most parts of that gene, so the body can’t produce the protein at all, while others have so many errors in the that the body eliminates the flawed protein as soon as it’s produced—but the researchers turned their attention to those genes that were full of errors, which made the body stop reading the blueprint so that it didn’t produce the protein.

In order to correct the errors in the genetic code, the researchers decided to simply cut them out. That would allow the body to keep reading the gene and create a shorter protein that still sort of works to protect muscles and prevents them from breaking down as quickly—just like patients with Becker muscular dystrophy, who retain their muscle function for longer than patients who don’t make any usable dystrophin protein.

In their experiments, the researchers loaded the CRISPR complex into a virus and injected it into mouse fetuses that had Duchenne muscular dystrophy mutations. And each time, the researchers found that, by using it to snip away the hindering mutations on that one gene, the mice started to make the truncated protein. That helped the mice retain the use of their muscles, effectively treating the disease.

Though the results are promising, they don’t necessarily mean that the treatment will be foolproof for humans. Though CRISPR can snip away additions to the dystrophin gene, it’s still not clear if it could help fix other types of mutations, such as filling in the gaps where mutations have caused genetic information to be dropped. That means that it might not be a viable treatment for all patients with the disease. The researchers are also unsure about how the virus, used to deliver the CRISPR complex, may react with the human immune system. Plus, there are still lots of ethical concerns about using CRISPR on humans.

This isn’t the first time researchers have tried to use gene therapy for Duchenne muscular dystrophy. But with additional research, there’s a chance that this could be the first time it succeeds—researchers are hoping to position themselves to start clinical trials within the next few years, according to the New York Times.