Dogs suffering from muscular dystrophy are having their genomes edited with CRISPR, and the results are “mind-blowing.”

Researchers from Texas this week unveiled data showing how CRISPR, a new tool for modifying genes, could reverse the molecular defect responsible for Duchenne muscular dystrophy, a devastating illness that affects about one in 5,000 boys.

The effort, led by Eric Olson of the University of Texas Southwestern Medical Center, is among of the first to try to use CRISPR to cure disease in a large, familiar animal.

If the treatment can stop muscular dystrophy in dogs, that would set the stage for giving the experimental treatment to boys, according to the research team.

Biotech companies are preparing to use CRISPR to treat human blood disorders like thalassemia, as well as liver ailments and genetic causes of blindness.

But muscular dystrophy could prove CRISPR’s most important test yet—and maybe its biggest payoff. That’s because the disease is relatively common and invariably fatal, and there is no treatment to stop it.

Olson has previously characterized CRISPR as a potential "cure" for the disease.

This week the Texas team began previewing its newest results. On Monday, during a conference at the National Institutes of Health, researcher Leonela Amoasii reported how the team had infused CRISPR into the bloodstream of one-month old puppies bred to suffer from the disease. It widely repaired the cells of their muscles and hearts, she said.

“We see widespread correction,” Amoasii said, flashing pictures of repaired cells. She called the clearly visible improvement "striking."

“In principle it’s a one-time treatment,” said Amoasii.

The effort is funded by Exonics, a young biotechnology company started by the patient advocacy group CureDuchenne in 2017, which has by now raised more than $40 million.

Olson’s lab previously reversed muscular dystrophy in mice. The move into dogs is important, though, since a treatment capable of curing dogs stands a good chance of helping humans, too.

Experiments on dogs carry public-relations risk. The animal rights group PETA in 2016 began a campaign against another Texas lab working on muscular dystrophy in dogs, and it is tracking gene editing as well.

Tasgola Bruner, a spokesperson for PETA, says the group is in favor of CRISPR but doesn’t want gene editing tested on animals.

Duchenne muscular dystrophy is caused by DNA spelling errors in a gene responsible for producing a protein called dystrophin. The giant protein acts like a shock absorber in muscle cells.

Without enough dystrophin, boys lose the ability to walk and eventually die of heart failure.

Scientists have long eyed whether the faulty DNA can be replaced using gene therapy, which involves employing viruses to add a healthy copy of a gene to people’s cells. The problem is the sheer size of the dystrophin gene. It’s one of the longest in the human genome—too large to pack inside a virus.

Several studies are under way to determine if a foreshortened “mini” version of the gene could help. Companies including SolidBio, Sarepta Therapeutics, and Pfizer are all testing therapies based on these shortened genes. Those tests advanced into human volunteers late last year.

Instead of adding a replacement gene, however, the CRISPR strategy entails using a virus to add the editing tool to a person’s body, where it can repair the genetic problem.

Restoring the function of a person’s own gene could be an advantage, though the challenge for gene editing is that more than 3,000 different mutations that can cause muscular dystrophy. Therefore, more than one CRISPR treatment will be needed to fix them all.

The teams at Exonics and in Texas are initially targeting one region of the gene, called exon 51, where a repair could help about 13 percent of patients. The company is also studying possible side-effects, such as immune reactions.

In the new research, Amoasii said, CRISPR was tested on dogs that are a mix between beagles and Cavalier King Charles Spaniels. She did not say if the dogs regained their strength or ability to run and play.