Duchenne Muscular Dystrophy Treatable with Modified Gene Engineering Therapy

A team of biomedical engineers has demonstrated the potential for curing Duchenne muscular dystrophy (DMD) with modified gene editing therapy that does not require a DNA repair template.

DMD is caused by mutations in the gene that encodes the protein dystrophin and the subsequent disruption of the dystrophin-associated protein complex (DAPC). The mutation occurs on the X-chromosome, and the disease effects about one of every 3,500 boys whose muscle function is so degraded that they die usually before reaching the age of 30.

Having based their experiments on the premise that many genetic diseases could be treated simply by correcting a disrupted DNA reading frame, investigators at Duke University (Durham, NC, USA) recently reported that genome editing with transcription activator-like effector nucleases (TALENs), without a repair template, could efficiently correct the reading frame and restore the expression of a functional dystrophin protein.

Restriction enzymes are enzymes that cut DNA strands at a specific sequence. TALENs can be engineered to bind practically any desired DNA sequence, and by combining such an engineered TALEN with a DNA cleavage domain (which cuts DNA strands), one is able to engineer restriction enzymes that are specific for any desired DNA sequence. When these restriction enzymes are introduced into cells, they can be used for genome editing in situ, a technique known as genome editing with engineered nucleases.

The Duke University investigators engineered a TALEN gene to mediate highly efficient gene editing at exon 51 of the dystrophin gene. The gene was inserted into plasmids, and the plasmids were used to transfect target cells including skeletal myoblasts and dermal fibroblasts. The TALENs were then used to edit the genome by inducing double-strand breaks (DSB), to which the cells responded with repair mechanisms.

Results published in the June 4, 2013, online edition of the journal Molecular Therapy revealed that genome editing with TALENs, but without a repair template, could efficiently correct the reading frame and restore the expression of functional dystrophin protein that had been mutated in DMD.

"Conventional genetic approaches to treating the disease involve adding normal genes to compensate for the mutated genes," said senior author Dr. Charles Gersbach, assistant professor of biomedical engineering at Duke University. "However, this can cause other unforeseen problems, or the beneficial effect does not always last very long. Our approach actually repairs the faulty gene, which is a lot simpler. It finds the faulty gene and fixes it so it can start producing a functional protein again."

"Similar approaches could be helpful in treating other genetic diseases where a few gene mutations are responsible, such as sickle cell disease, hemophilia, or other muscular dystrophies," said Dr. Gersbach.

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