Gene Editing Method Corrects Mutations in Duchenne Muscular Dystrophy

Eric Olson, PhD

Scientists from UT Southwestern Medical Center have developed a CRISPR gene-editing method that has the ability to correct 3,000 mutations that lead to Duchenne muscular dystrophy (DMD).

Using heart muscle cells (cardiomyocytes) taken from patients with DMD, the researchers found that a single cut in strategic locations in the DNA could offer an efficient substitute to developing individualized molecular treatments for each of the mutations that cause the condition.

“This is a significant step,” Eric Olson, PhD, the director of UT Southwestern’s Hamon Center for Regenerative Science and Medicine, said in a statement. “We’re hopeful this technique will eventually alleviate pain and suffering, perhaps even save the lives, of DMD patients who have a wide range of mutations and, unfortunately, have had no other treatment options to eliminate the underlying cause of the disease.”

Previous work done by Olson and colleagues using the CRISPR-Cas9 gene-editing tool allowed for the correcting of a single mutation that caused DMD, with this work building on that.

"[This achievement is] huge, CRISPR/Cas9 has fundamentally changed biomedical science," Olson told MD Magazine. "We are building upon decades of science seeking to understand the structure and function of the human genome in health and disease, we now have tools to manipulate it, therapeutically, in a way never before imagined. It's an astounding advance in technology."

Using a dozen RNAs as guides for the Cas9 enzyme, the team was able to pinpoint so-called “hotspots” along the dystrophin gene, where up to 60% of mutations are located, that allowed for restoration of cardiac function to near-normal levels in the heart muscle tissue.

Abnormal splice sites in the DNA results in the irregular dystrophin molecules, but editing those sites out gave the genetic machinery the ability to express improved dystrophin proteins. These single-cut editing methods may be effective for other single-gene diseases, but for it to be successful, the genes involved must be able to function if certain exons are removed from the protein formula.

“This is a new concept,” Rhonda Bassel-Duby, PhD, a co-author of the study and professor of Molecular Biology at UT Southwestern said in a statement. “Not only did we find a practical way of treating many mutations, we have developed a less disruptive method that skips over defective DNA instead of removing it. The genome is highly structured, and you don’t want to remove DNA that could potentially be important.”

The researchers only needed to correct from 30% to 50% of the cardiomyocytes to rescue the mutant phenotypes, said Chengzu Long, PhD, the lead author and an assistant professor of medicine at New York University Langone Health.

Pending approval from the US Food and Drug Administration, the researchers are anticipating that clinical trials involving CRISPR use in blood disorders will begin this year. Olson's lab at UT Southwestern is reportedly planning to continue to test the method to improve precision and ensure it does not result in adverse events.

"There are hundreds if not thousands of gene mutation-based human diseases, ranging from sickle cell anemia to DMD, which might be addressed by CRISPR/Cas9 somatic cell gene editing," Olson said. "Certainly fundamental hurdles remained to be overcome, [such as] how to deliver the CRISPR/Cas9 gene editing machinery to large human organs like the heart or skeletal musculature or how to ensure safety, maintaining the integrity of the genome, yet this exciting new technology for the first time ever should allow us to permanently 'fix' genetic errors in the human genome itself, at the DNA root cause of the clinical problem. This will fundamentally change our approach to many diseases, indeed raising the possibility of genetic cures—a word we generally don't like to use in medicine."

As for the timeline, Olson noted that while some believe this method of myoediting could be used routinely within the next 5 years, that is most likely not the case. "This is optimistic but not unrealistic given the current pace of this science, it will be at the bedside soon. Of course, priority will be given to treating young patients (like at-risk children) who will benefit most, before irreversible tissue destruction has occurred, from myoediting," he said.

The study, “Correction of diverse muscular dystrophy mutations in human engineered heart muscle by single-site genome editing,” was published in Science Advances.

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