Fighting fire with fire, researchers working with dogs have fixed a genetic glitch that causes Duchenne muscular dystrophy (DMD) by further damaging the DNA. The unusual approach, using the genome editor CRISPR, allowed a mutated gene to again make a key muscle protein. The feat—achieved for the first time in a large animal—raises hopes that such genetic surgery could one day prevent or treat this crippling and deadly disease in people. An estimated 300,000 boys around the world are currently affected by DMD.
The study monitored just four dogs for less than 2 months; more animal experiments must be done to show safety and efficacy before human trials can begin. Even so, “I can’t help but feel tremendously excited,” says Jennifer Doudna of the University of California, Berkeley, who heard the results last week at a CRISPR meeting she helped organize. “This is really an indication of where the field is heading, to deliver gene-edited molecules to the tissues that need them and have a therapeutic benefit. Obviously, we’re not there yet, but that’s the dream.”
Mutations in the gene encoding dystrophin, a protein that maintains muscle integrity and function, cause Duchenne muscular dystrophy (DMD). The deltaE50-MD dog model of DMD harbors a mutation corresponding to a mutational “hot spot” in the human DMD gene. We used adeno-associated viruses to deliver CRISPR gene editing components to four dogs and examined dystrophin protein expression 6 weeks after intramuscular delivery (n=2) or 8 weeks after systemic delivery (n=2). After systemic delivery in skeletal muscle, dystrophin was restored to levels ranging from 3 to 90% of normal, depending on muscle type. In cardiac muscle, dystrophin levels in the dog receiving the highest dose reached 92% of normal. The treated dogs also showed improved muscle histology. These large animal data support the concept that, with further development, gene editing approaches may prove clinically useful for the treatment of DMD.