Genome Editing Cures Muscular Dystrophy in Mice

Researchers from Duke University have used the CRISPR technology to cure Duchenne muscular dystrophy in a mouse. It is the first time that the gene editing technology is successfully used to treat an adult mammalian. The study, published in the journal Science, establishes CRISPR/Cas9 as a potential therapy for the treatment of muscular dystrophy in humans.

Duchenne muscular dystrophy (DMD) is an inherited disorder caused by mutations in the dystrophin gene, which codes for a muscle protein. It affects 1 of every 3600 male births, causing them fatigue, muscle weakness and intellectual disability. The CRISPR technology, heralded as the scientific breakthrough of 2015, allows accurate gene editing on eukaryotic cells. Duke researchers had previously used CRISPR in vitro to edit the mutations in cells from Duchenne patients. Other researchers had eliminated the mutations from single-cell embryos, also in vitro. These approaches involve ethical and practical issues that make them currently unsuitable for DMD treatment in humans. For example, inserting the CRISPR system in the cells by electroporation -poking holes in the cell membrane using electricity- works in vitro, but not in vivo. In an alternative method for DMD treatment, gene therapy, there are also problems to deliver the genes to the cells.

Using an adeno-associated virus and a smaller endonuclease

The main problem when using gene editing technologies is delivering them to the cells. Dr. Charles Gersbach and his team took advantage of viruses, who have been shaped by evolution for billions of years to introduce their genetic material into cells. They delivered CRISPR to a Duchenne-affected mouse via the non-pathogenic adeno-associated virus (AAV). AAV is already being used in clinical trials in the US and has been approved for use in gene therapy in Europe. However, AAV is relatively small, and the canonical CRISPR/Cas9 system doesn’t fit due to the big size of Streptococcus pyogenes’ Cas9. The researchers solved this by looking for a smaller endonuclease, and found it in Staphylococcus aureus. The new CRISPR/Cas9 tandem was injected in the sick mouse’s bloodstream. The system excised the mutated region, and the DNA break was repaired by endogenous DNA damage repair mechanisms. The mouse showed a remarkable improvement in muscle strength in the whole body.

In the future, the Duke researchers plan to optimize the system delivery, test its efficiency on severe cases of DMD, and conduct trials in bigger mammals, eventually including humans.

Source: Duke