Muscular Dystrophy Treatment with CRISPR Technology on the Way

Adeno-associated virus—mediated (AAV-mediated) CRISPR gene editing technology can eventually be used in the treatment of Duchenne muscular dystrophy, according to recent findings. Although CRISPR is often used to treat inherited diseases—not chronic conditions—that could be changing soon.

In children, muscular dystrophy causes a gene mutation that inhibits production of the dystrophin protein. Without dystrophin, muscles weaken and die, leaving children unable to walk or without muscles related to breathing and heart function.

Investigators from the University of Missouri School of Medicine conducted a study in mice models to first test this process of gene editing using CRISPR. The team treated 6-week-old mice with Duchenne muscular dystrophy and followed up at 18 months.

Study leader Dongsheng Duan, PhD, explained to Rare Disease Report® that CRISPR is moving quickly toward becoming a therapy for Duchenne muscular dystrophy as well as other rare diseases.

“Ideally, one would like to have long-lasting benefits from a single treatment,” Duan said. “Unfortunately, it has never been tested whether a single CRISPR therapy can lead to long-term disease amelioration. Our study addressed this key issue.”

At first, the investigators used the CRISPR technique commonly used in studies, which has been shown to ameliorate disease in the short-term. It seemed successful when injected directly into the muscle, the investigators reported. However, when they tried to achieve long-term success in all of the mice’s muscles, it didn’t work as well, resulting in nominal CRISPR editing in skeletal muscle, limited dystrophin restoration in the heart, and no improvement in cardiac histology and hemodynamic function.

Instead, they changed their strategy to increase the number of gRNA, which tells the CRISPR Cas9 “scissors” where to “cut.” With that, they were able to increase the dystrophin restoration in the heart and skeletal muscles in the mice after 18 months. The investigators also observed improved muscle and cardiac function.

In more technical terms, as Duan explained, “Through mechanistic studies, we found that long-term systemic therapy requires administrating high amount of the gRNA vector. We then modified our approach by co-injecting the Cas9 and gRNA vectors at a 1:3 ratio. This resulted in significantly much higher dystrophin restoration and improvement of both skeletal muscle and heart function.”

The investigators said their findings overcome a hurdle specific to CRISPR therapy treatment, when increasing gRNA levels to reach optimal amounts. They will continue to test and refine their method in mice models before exploring and expanding to other research.

“Our study reveals an important hurdle that has not been appreciated in all previous studies,” Duan said. “The approach we developed may be used to achieve long-term therapeutic benefits for Duchenne muscular dystrophy and many other diseases.”

The study, titled “AAV CRISPR editing rescues cardiac and muscle function for 18 months in dystrophic mice,” was published in the journal JCI Insight.