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Gene therapy for dogs

The focal defect in type 1 Diabetes Mellitus (DM) is the inability to control glucose levels in the body due to a lack of insulin. Insulin is usually the mediator of glucose levels in the blood; the cause of type 1 DM is the destruction of insulin-producing beta cells in the pancreas by the body’s own immune system. This form of diabetes is not preventable or curable in humans, and affects approximately 20 million people worldwide, many of these are children or adolescents; therefore it is important that scientists are conducting experiments in the hopes of finding a cure. Current treatment for diabetes involves insulin replacement therapy either through injection or a pump, using biosynthetic analogs of insulin. The primary goal of the treatment is to normalise blood glucose levels to prevent the symptoms of DM (excessive thirst and urination, weight loss and fatigue) and prevent the more serious consequences, such as hyperglycaemic coma and death. However, this is not even close to an adequate solution to DM as it requires lifelong meticulous management and can contribute to mental illness in diabetic patients; a prime example being depression, which is much more prevalent in diabetics than non-diabetics. Eating disorders can also arise in people living with diabetes.

A cure is not such a distant possibility for type 1 DM as researchers at a university in Barcelona recently reported that they had cured this disease in Beagles. Although DM has been cured before in mice, it is an entirely new achievement to have cured this in a large animal.It was achieved by using a relatively new technique called gene therapy. Gene therapy usesmodified viruses to insert desired genes into target cell genomes (the DNA in cells). Viruses are very useful organisms for delivering genes because some types of virus naturally insert their genomes into host cell genomes when they need to replicate their DNA; the viruses used here are modified so that they can insert their genome into the host genome but cannot cause any damage after this. Scientists can use this medically to correct genetic mutations that result in disease by replacing the faulty genes in patients with functional ones; research is currently investigating the use of gene therapy to potentially cure type 1 DM, cystic fibrosis, haemophilia and sickle cell anaemia.

For this experiment a small number of beagles were given chemicals to destroy their pancreatic beta cells, therefore inducing type 1 DM. Then they were subjected to gene therapy. The genes inserted coded for an enzyme called glucokinase, involved in the processing of glucose, and a “glucose sensor” which would monitor the glucose levels in the blood. The viral vector containing these genes was injected in multiple places in the rear legs of the dogs; this process was carried out a single time. It was reported that the genes successfully incorporated into the dogs’DNA and were being expressed, at this point the dogs no longer showed symptoms of DM. This was so successful in fact that the dogs were still healthy four year later, proving that gene therapy can be used as a cure for diseases that result from genetic mutations. Interestingly inserting only one of the genes did not yield any health benefits in the dogs. This suggests that for the genes are synergistic and so must both be present for therapy to work.

The results of this experiment cannot be extrapolated to human tests though, because the initial induction of type 1 DM in dogs was different to how it arises in humans. Nevertheless, if this therapy proves successful upon further testing, trials will begin on human patients.Successful clinical trials would mean that this could be publicly available as a treatment option within ten years, an exciting prospect for sufferers of type 1 DM.

The original journal article can be found at: http://diabetes.diabetesjournals.org/content/early/2013/01/30/db12-1113

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