Genetics

Urban Jungle

PUBLISHED : Friday, 20 June, 2008, 12:00am
UPDATED : Friday, 20 June, 2008, 12:00am

This week: gene therapy

It is just phenomenal how far science has come in the past 10 years, especially in the area of biotechnology, and in particular, genetic engineering and molecular biology. I remember that when I first decided to leave my mathematics and physics career to pursue a biology-based one, I was enticed by a new course on offer called 'genetics'. It was a burgeoning science at the time and much of it was in the area of research rather than applications. Coming from a maths and physics background, I'd had enough of the theoretical and wanted more application, so this led me into a career in veterinary science.

There was certainly a small element of genetics taught at vet school, but it didn't have many real life applications at the time, and was mostly limited to how some diseases were genetically inherited and how some were due to mutations of existing viruses or other microbes. We had a firm grounding in the area of how genes replicate and how they operate.

It was announced in 2006 that scientists had for the first time a completely mapped out gene of a boxer and 80 per cent of a poodle. These molecular biologists hope one day this will play a role in the understanding and eventual development of treatments for diseases of dogs. Since many diseases like cancer, epilepsy and diabetes are shared by humans, they hope that by understanding the dog's genome we will have insight into the human genome.

Dogs as a species have many physical and behavioural differences, due to selective breeding since domestication. This selective breeding has caused some breeds of dogs to be more predisposed to certain disorders, such as cancer, heart diseases, blindness, hormonal imbalances and many others. It is easier to identify defective genes in dogs by comparing different breeds. It is much harder to do a primary study in humans, as we don't have many close genetic relatives with which to compare. There are about 19,300 genes in the dog's genome and many of these correspond to similar genes in humans. So knowing the dog's genomic problems will lead to a further understanding of human genomic problems.

In this decade, a new technique in treatment was developed called gene therapy. Previously relegated to the realms of science fiction, this form of treatment uses engineered genes transplanted into living cells in the body to help fix problems. One of the major breakthroughs and useful applications of this procedure was the treatment of haemophilia, an inherited blood disorder that meant the blood of people with it would not clot, even after minor cuts. A defective gene that stopped producing a vital protein in the blood-clotting pathways caused the problem. What scientists did was introduce DNA that contained this protein-making gene into living cells of the patient, so the patient was then able to produce the protein, hence curing a once incurable disease.

Everyone has heard 'bubble boy' stories about children whose immune systems were so defective that they were easily infected with simple diseases that could be fatal. These children led isolated lives and often didn't survive into adulthood. Scientists found the defective gene, and with the use of gene therapy and the reintroduction of an effective gene, these children could lead an almost normal life. But the treatment needed to be repeated to sustain the immune system. The short-lived nature of gene therapy is one of its current drawbacks.

What brought about this line of thought was an article by a pharmaceutical company in Texas about a new gene therapy that can help dogs with cancer live longer with better quality of life. This obviously has implications in the field of human oncology.

I have many patients - dogs, cats, rabbits and other exotics - that come down with a condition called cancer cachexia. It causes severe weight loss and muscle wasting despite an often normal appetite. To put it simply, the cancer in animals draws nutrients away from the animal's normal systems and eventually causes the animal to become very weak and sick. This fatigue causes a poor quality of life during the final stage of life and the animal is less likely to respond to more traditional cancer therapy, such as chemotherapy.

These scientists discovered a way to trick the body into producing more endogenous hormones, which promote muscle growth and hence help fight off cancer cachexia. Dogs under the therapy lived 84 per cent longer than dogs that did not have it. And they lived happier and more normal lives, and had fewer complications from chemotherapy.

So, in the relatively short span of my veterinary career, genetics have come a very long way from being a theoretical novelty to what now seems to be limitless possibilities in treatment, both veterinary and human.