CRISPR Research Might Lead to Cure for Duchenne Muscular Dystrophy

At this time, there is no cure for Duchenne muscular dystrophy (DMD), although there is one treatment for a subgroup of the disease. That is Sarepta Therapeutics’ Exondys 51 for DMD patients with a confirmed mutation amenable to exon 51 skipping. Recently the U.S. Food and Drug Administration (FDA) rejected Sarepta’s golodirsen for DMD with a confirmed mutation appropriate for exon 53 skipping.

DMD is a muscle wasting disease caused by mutations in the dystrophin gene. It is a progressive disease that usually causes death in early adulthood, with serious complications that include heart or respiratory-related problems. It mostly affects boys, about 1 in every 3,500 or 5,000 male children.

There just might be, however, hope for an actual cure. Researchers at the University of Missouri-Columbia, utilized CRISPR gene editing in a mouse model, to edit out the gene mutation and transplant AAV9 treated muscle into the mice. The transplanted muscle cells carried the edited gene and successfully produced dystrophin, the protein that is not produced in sufficient quantities in DMD patients.

The dystrophin gene is the largest in the body, and codes for the dystrophin protein, which is involved in muscle development and activity. One of the reasons DMD has been a tough nut to crack is that because of the gene’s size, it’s too large to fit into the typical viral vectors used in gene therapies. That’s partially why Sarepta’s approach is to use a type of RNA splicing that forces cells to “skip” over the faulty section of genetic code. This results in a shortened (truncated) protein that is still functional.

“Research has shown that CRISPR can be used to edit out the nutation that causes the early death of muscle cells in an animal model,” said Dongsheng Duan, the Margaret Proctor Mulligan Professor in Medical Research in the Department of Molecular Microbiology and Immunology at the MU School of Medicine and senior author of the study.

“However,” Duan went on, “there is a major concern of relapse because these gene-edited muscle cells wear out over time. If we can correct the mutation in muscle stem cells, then cells regenerated from the edited stem cells will no longer carry the mutation. A one-time treatment of the muscle stem cells with CRISPR could result in continuous dystrophin expression in regenerated muscle cells.”

Duan’s research, in collaboration with others at MU as well as the National Center for Advancing Translational Sciences, Johns Hopkins School of Medicine and Duke University, looked at whether muscle stem cells in mice could be effectively edited. They used AAV9, an adeno-associated virus recently approved by the FDA to treat spinal muscular atrophy (SMA)—Novartis’ Zolgensma, which is also the source of the controversy over the company’s data manipulation scandal.

They started by delivering CRISPR to normal mouse muscle via AAV9.

“We transplanted AAV9-treated muscle into an immune-deficient mouse,” said Michael Nance, an MD-PhD program student in Duan’s lab and the lead author of the paper. “The transplanted muscle died first then regenerated from its stem cells. If the stem cells were successfully edited, the regenerated muscle cells should also carry the edited gene.”

That appeared to work. They then tested if the muscle stem cells in the mice of DMD could be edited with CRISPR—they were.

“This finding suggests that CRISPR gene editing may provide a method for lifelong correction of the genetic mutation in DMD and potentially other muscle diseases,” Duan said. “Our research shows that CRISPR can be used to effectively edit the stem cells responsible for muscle regeneration. The ability to treat the stem cells that are responsible for maintaining muscle growth may pave the way for a one-time treatment that can provide a source of gene-edited cells throughout the patient’s life.”

The research was published in the journal Molecular Therapy.