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Gene editing of dogs offers hope for treating human muscular dystrophy

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."

[...] The study offers little evidence that dogs regained muscle function, however, and that, coupled with the short duration of the study and the small number of animals studied, left some scientists less enthusiastic. One researcher in the tight-knit DMD field who asked not to be named wonders whether the study was rushed to help draw investment in Exonics Therapeutics, a Boston-based company Olson launched last year to develop the potential treatment.

[...] Another challenge was to alter billions of muscle cells throughout a living animal. So the team enlisted a helper: a harmless adeno-associated virus that preferentially infects skeletal muscle and heart tissue. Two 1-month-old dogs received intramuscular injections of the virus, engineered to carry CRISPR's molecular components. Six weeks later, those muscles were making dystrophin again. Those results led the researchers to give an intravenous infusion to two more dogs, also 1 month old, to see whether the CRISPR-carrying viruses could add the genome editor to muscles throughout the body. By 8 weeks, Olson told the meeting, dystrophin levels climbed to relatively high levels in several muscles, reaching 58% of normal in the diaphragm and 92% in the heart. But because the dogs were euthanized, Olson could show little evidence that they had avoided DMD symptoms, save for a dramatic video of a treated dog walking and jumping normally.

Also at Science News.

Gene editing restores dystrophin expression in a canine model of Duchenne muscular dystrophy (DOI: 10.1126/science.aau1549) (DX)

More about Duchenne muscular dystrophy at Wikipedia.

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