A new study conducted at the University of Missouri, USA, showed that it is possible to transfer a small version of the dystrophin gene to all muscles in the body of dogs without any side-effects.
The scientists used a harmless virus called an adeno-associated virus (AAV) as a carrier to deliver the miniature version of the gene to all muscles in the dog’s body including the heart and the diaphragm. This version of the gene called micro-dystrophin has all the necessary parts to make a functional dystrophin protein.
This approach has many challenges due to the fact that:
- The dystrophin gene is too large to fit inside the AAV
- It is difficult to deliver the gene to all parts of the body of especially large mammals
- The virus can trigger an immune response that results in its destruction
The results of the study are encouraging although more research is needed to assess the long-term safety and benefit of this approach. The researchers hope that if this success continues they could see clinical trials, using this approach, in humans in the coming years.
The aim of the research was to test whether it is possible to deliver a functional copy of the dystrophin gene to all muscles in a large animal model of Duchenne muscular dystrophy without harmful side-effects.
A number of studies have previously shown that this approach has been successful in a mouse model for Duchenne muscular dystrophy. However the mouse is not regarded as the best model of the condition because it does not reflect the severity of the symptoms seen in humans.
In order to better understand how well this technique could work in humans, the scientists repeated the experiments in a dog model of the condition that have symptoms more similar to those seen in humans.
The researchers modified the virus in a way that made it less likely to be detected by the immune system and be destroyed, and easier to be taken up by the body.
They injected three dogs born with muscular dystrophy when they were about two months old.
The study showed that:
- The injection was safe and did not result in any side effects.
- The micro-dystrophin gene was present in all muscles including the heart and the diaphragm.
Even though more research is needed to test the long-term safety and efficacy of the gene therapy approach, this piece of work has shown for the first time that it is possible to transfer a miniature version of the dystrophin gene to all the muscles of a large mammal. This could mean that it might also be feasible in humans.
The team at the University of Missouri state that clinical trials are being planned in the next few years to test this approach in people affected by Duchenne muscular dystrophy.
It is encouraging that this gene therapy approach is also being used for other conditions such as spinal muscular atrophy and is already in early clinical trial stage. Preliminary results from such trials support the idea that the approach could be applied to Duchenne muscular dystrophy.
Duchenne muscular dystrophy is caused by a mutation in the dystrophin gene. This leads to the lack of the vital muscle protein dystrophin. In the absence of dystrophin protein, muscles get damaged at each contraction and waste over time.
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