dystrophy. Research Current research includes exon-skipping, stem cell replacement therapy, analog up-regulation, gene replacement, and supportive care to slow disease progression. Efforts are ongoing to find medications that either return the ability to make dystrophin or utrophin. Other efforts include trying to block the entry of calcium ions into muscle cells. Exon-skipping Antisense oligonucleotides (oligos), structural analogs of DNA, are the basis of a potential treatment for 10% of people with DMD. The compounds allow faulty parts of the dystrophin gene to be skipped when it is transcribed to RNA for protein production, permitting a still-truncated but more functional version of the protein to be produced. It is also known as nonsense suppression therapy. Two kinds of antisense oligos, 2'-O-methyl phosphorothioate oligos (like drisapersen) and Morpholino oligos (like eteplirsen), have tentative evidence of benefit and are being studied. Eteplirsen is targeted to skip exon 51. "As an example, skipping exon 51 restores the reading frame of ~ 15% of all the boys with deletions. It has been suggested that by having 10 AONs to skip 10 different exons it would be possible to deal with more than 70% of all DMD boys with deletions." This represents about 1.5% of cases. People with Becker's muscular dystrophy, which is milder than DMD, have a form of dystrophin which is functional even though it is shorter than normal dystrophin. In 1990 England et al. noticed that a patient with mild Becker muscular dystrophy was lacking 46% of his coding region for dystrophin. This functional, yet truncated, form of dystrophin gave rise to the notion that shorter dystrophin can still be therapeutically beneficial. Concurrently, Kole et al. had modified splicing by targeting pre-mRNA with antisense oligonucleotides (AONs). Kole demonstrated success using splice-targeted AONs to correct missplicing in cells removed from beta-thalassemia patients Wilton's group tested exon skipping for muscular dystrophy. Gene therapy Researchers are working on a gene editing method to correct a mutation that leads to Duchenne muscular dystrophy (DMD). Researchers used a technique called CRISPR/Cas9-mediated genome editing, which can precisely remove a mutation in the dystrophin gene in DNA, allowing the body's DNA repair mechanisms to replace it with a normal copy of the gene. The benefit of this over other gene therapy techniques is that it can permanently correct the "defect" in a gene rather than just transiently adding a "functional" one. Genome editing through the CRISPR/Cas9 system is not currently