The idea of gene therapy sounds like something straight from a science fiction story. It involves replacing some of the genes inside a cell to change its function, resulting in improvement or resolution of a medical condition. This treatment method is being explored more and more, and the results in dogs have been very positive.
As the name suggests, gene therapy is designed to treat genetic diseases. The goal of treatment is to correct the genetic defect that’s the cause of a disease and resolve it completely without the need for ongoing drug therapy. Defective genes are identified and are replaced with a properly functioning gene that makes the cell work normally again. The normal gene is attached to a vector (or carrier) which is a virus that has been inactivated and is completely harmless. The vector is then injected into the patient and carries the gene to the defective tissue. When the vector gets inside the cell, the replacement gene is incorporated into its genetic material, resulting in a normally functioning cell.
There are a number of medical conditions where scientists are seeing gene therapy work well in dogs, and the outcome of these studies can then help humans with genetic conditions.
- Muscular dystrophy in people and dogs is associated with an abnormal dystrophin gene. Dystrophin is a protein that’s involved in muscle structure and without it, muscle cells gradually die. Scientists at the University of Missouri have injected a dystrophin microgene into dogs with Duchenne muscular dystrophy – the most common form of the muscular dystrophy disease. Afterwards, they found that normal dystrophin protein was detected in the dogs’ muscles for several months after the injection. There was also evidence that the muscle tissue had actually improved when looked at under the microscope.
- Researchers at the Autonomous University of Barcelona injected diabetic dogs with two genes involved in glucose metabolism. The genes entered the muscle cells and released insulin and glucokinase, which are both involved in maintaining blood glucose levels. In this study, the dogs’ blood glucose remained within normal limits for around four years after the injection.
- X-linked retinitis pigmentosa is a cause of blindness in dogs, and is associated with a mutation in a gene known as RPGR. Scientists funded by the National Eye Institute injected a normal copy of this gene into the dog’s eye, between the retinal layer and the layer of photoreceptor (or light-detecting) cells. The photoreceptor cells then started producing normal RPGR protein that prevented degeneration in those parts of the retina that were treated. This result can give hope to people afflicted with a similar genetic blindness.
In spite of these outcomes and the amazing potential of this type of treatment, gene therapy still has limitations. Many diseases are caused by multiple gene abnormalities instead of a mutation in just one gene. It’s easier to manage diseases that have single gene mutations. Similarly, the severity of some medical conditions can be affected by environmental factors and these are less responsive to gene therapy. Scientists need to fully understand the genetics behind a disease and know the exact gene that’s causing the problem so they can replace it. Lastly, as can be seen from the muscular dystrophy and diabetic studies, there may be a need for further injections of genes depending on the duration of the effect of treatment.
There is much yet to learn about gene therapy, but it appears to be a very promising treatment that corrects the basic cause of a genetic disease, with no adverse effects. The results of the studies in dogs can be adapted to humans and it’s hoped that the outcomes will be just as positive.