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The Genetics of Canine Aging and Longevity

05/17/2005
Author: Sarah Canterberry

It is a well-known phenomenon among owners and breeders that purebred dogs exhibit a decrease in life expectancy as the breed size increases.  This trend is quite opposite what is seen among mammals of different species.  For example, small animals such as mice may be expected to live only a few years while their larger counter parts, like elephants, may live as long as 70 years or more.  Researchers at Texas A&M University College of Veterinary Medicine believe that this unexpected trend seen in the dog is due in part to underlying genetic factors.  The long-term objectives of their work include assessment of genes most likely to affect the aging process in the dog.  These scientists plan to characterize genes in the dog that appear to be linked to the aging process in an attempt to increase not only the lifespan of our canine companions, but to also improve the quality of life for dogs in the geriatric population.

The initial step in this process has been to determine the exact effect size has on canine longevity.  Data was collected primarily from internet sources on average height and weight standards, as well as the average life expectancy of pure breed dogs.  Preliminary regression analysis of 117 breeds supports what veterinarians and dog owners alike have suspected for many years: as the average size of a dog breed increases, the average life expectancy decreases. 

Next, the chromosomal locations of 54 genes were compared between the human and the dog.  Included in this study were 26 genes that had been shown to affect the life expectancy of either humans or mice, as well as 28 genes located in a small region of human chromosome 4.  This region was selected for detailed mapping because it has been shown to associate with the ability to reach excessive old age in a human population.  

On-going work is being focused in two areas.  One interest is in defining single nucleotide polymorphisms (SNPs), which are single base pair changes, in 7 genes of interest selected from the previously mentioned set of genes.  Analysis of these SNPs across various breeds has the potential to identify genes that cause larger dogs to experience a shorter life span in comparison with their smaller counterparts.  DNA samples have been collected, in the form of buccal swabs, from dogs of different sizes and different life expectancies.  These samples will be used to compare the aforementioned genes between these diverse breeds in hopes of discovering genetic factors that contribute to the aging process in the dog. 

The other primary interest of scientists is to discover the effects oxidative stress has on the aging process in various dog breeds.  Oxidative stress has been shown to affect the aging process in a variety of model organisms including mice, fruit flies and worms.  Studies in humans have also implicated oxidative stress as one of the causative factors in the aging process.  By investigating oxidative stress in our canine companions, researchers hope to discover mechanisms that allow different breeds to overcome oxidative stress more efficiently than others.  Primary cell cultures are being grown from donated skin samples and are being exposed to different forms of oxidative stress.  Assessments will be made to determine if there is any correlation between the size of the breed that donated the initial skin sample and the reaction of the cells to the oxidative stress event.

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