Genetics

Pet Tales
by Barry B. Burtis D.V.M.


Genetics is quite a complex science. While there is yet very much to learn about genes and how they influence life, we know much more today than we did just a few years ago. This increased learning has already and will continue to impact tremendously on the practice of medicine - both human and veterinary.


In 2003, a 99% complete map of the human genome was announced. A genome is the order of the genes or the full DNA sequence of an organism. It is the complete genetic information of that organism. The human genome is composed of about 3 billion base pairs, of which only about 2% forms coding DNA (genes); the rest is non-coding and serves various functions, such as gene regulation. Humans have about 20 - 25,000 genes.The function of 50% of those genes is still unknown. It required a tremendous effort to create that human gene map. The cost was approximately $2.7 billion and the project took a consortium of 20 groups 13 years to complete it. In 2005, the National Human Genome Research Institute (NHGRI) announced a light coverage map of the feline genome (2 - fold; capturing about 80% of the genome) had been made. In 2009, the NHGRI funded an effort to improve the genome coverage from 2-fold to 10-fold. The feline genome also has about 3 billion base pairs. Improving the detail in this feline map will require the collective resources of sequencing facilities, genetic mappers, geneticists, veterinarians and others in the coming years.


There are about 250 genetic diseases known to affect cats. Many of these diseases are very similar to human diseases. In fact, the cat serves as an animal model for about 200 human diseases. Genetic research focuses not only on inherited diseases, but also on infectious diseases, such as feline immunodeficiency virus (FIV). A cat infected with this virus can suffer from the same health problems that can affect people infected with the human immunodeficiency virus (HIV). Hence, FIV infection can act as a model for study of HIV.


Even the genes responsible for coat colours are being identified and may have medical implications. Perhaps we will learn more about the deafness that can affect white cats. It's quite certain that as work on the feline genome progresses, more single gene trait diseases will likely be identified. There are also a number of feline diseases that we suspect have a genetic component, though at present that component appears complex and not well understood. Feline infectious peritonitis, diabetes and feline asthma would be examples of such diseases. Cats are most frequently affected by Type 2 or non-insulin dependent diabetes. This form of diabetes also commonly affects humans. It's another case where learning more about an illness in one species will likely be beneficial to another species.


At the present time, there are more than one dozen genetic tests available for the cat, including tests for blood type and some coat colours. As our knowledge about inherited and genetic disease in cats increases, veterinarians and others involved in their health care will undoubtedly have new avenues of treatment for their patients open up. Gene therapy will probably offer possibilities for preventions and cures, not even thought of today. It is definitely a future likely to be filled with excitement.


Next time, I want to write more about inherited diseases. Hypertrophic cardiomyopathy, a type of heart disease, and polycystic kidney disease are such diseases that can affect cats and will be discussed. Barry Burtis is a local companion animal veterinarian. Past Pet Tales can be found at www.baycitiesanimalhospital.ca.