Gene therapy is a promising treatment option for genetic conditions such as muscular dystrophy. It involves correcting the genetic defect by introducing a normal copy of the affected gene into the patient’s cell or by silencing a faulty gene.
Harmless modified viruses are commonly used for the targeted delivery of healthy genes into the body. The adeno-associated virus (AAV) is one such delivery vector, and several AAV-mediated gene therapy candidates are currently being evaluated as potential treatments for muscular dystrophy.
Dystrophin is a muscle protein that provides structural support to the muscles protecting them from damage. A mutation in the DMD gene, which carries instructions for dystrophin, causes a lack of the protein, leading to muscle wasting seen in patients with the most common type of muscular dystrophy, Duchenne muscular dystrophy. Three AAV-based gene therapy candidates are designed to rectify this defect directly while another one aims to increase the production of other proteins that are important for muscle health.
SRP-9001 micro-dystrophin is a therapeutic candidate being developed by Sarepta Therapeutics and the Nationwide Children’s Hospital to treat people with DMD. It is designed to deliver a gene that encodes for so-called microdystrophin protein directly to the muscle tissues. This gene is similar to the DMD gene but is smaller in size, which provides an advantage for its targeted delivery to muscle cells. Microdystrophin is also smaller than dystrophin but has been modified for improved function. This gene therapy uses a modified AAV vector — AAVrh74 — which has a high affinity for muscle cells.
PF-06939926 is a gene therapy candidate being developed by Pfizer for the treatment of DMD. It also delivers a shortened version of the DMD gene that encodes for so-called mini-dystrophin protein, which is smaller than dystrophin but still functional. PF-06939926 uses AAV9 vectors for gene delivery to the muscles.
GALGT2 is an AAV-based therapy candidate that is also being developed in a collaboration between Sarepta Therapeutics and the Nationwide Children’s Hospital. It’s designed to deliver the GALGT2 gene rather than a smaller version of the DMD gene to the patient’s body. The GALGT2 gene carries instructions for a protein that increases the production of other proteins necessary for muscle strength and function. rAAVrh74.MCK.GALGT2 is considered a surrogate therapy because it aims to compensate indirectly for missing dystrophin by enhancing the production of other proteins involved in muscle regeneration.
Last updated 07/15/2019
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