The Scary Reality of Dog Genetic Disease

The prevalence of genetic disease in dogs today can only be described as alarmingly common which is bad news for dog owners and dog lovers alike. The following is a list to illustrate the magnitude of the problem:

1. On average all dogs carry at least 4-5 defective genes.

2. Over 500 genetic diseases have been identified in dogs.   

3. Hip Dysplasia (HD) (an inherited orthopedic disease that may result in the dog becoming lame) commonly occurs in 60 dog breeds and occurs less frequently in another 110 breeds; thus this disease is seen in over 170 breeds of dog.

4. 119 dog breeds are commonly afflicted with progressive retinal atrophy (PRA), a disease that quite often leads to blindness in the affected animal.

5. Of all the dog breeds the Poodle suffers from the most number of genetic diseases...145! The reason why the Poodle is predisposed to so many genetic diseases is because not only are there 3 distinct sizes of Poodle in this breed, the large count of disease is a reflection of the popularity of this dog breed. By and large a good rule of thumb is, the more popular a dog breed the greater the number of genetic diseases inherent in that breed.

6. Several popular dog breeds are linked to over 100 genetic diseases.

7. These days dog breeders spend well over $500,000,000 annually in an effort to address this disturbing trend of genetic disease in man's best friend.

As it is all the various dog breeds that exist today were artificially created; in other words each and every dog breed was selectively bred for a particular trait, be it coat color, coat length, sniffing ability, shortness of stature (miniatures), facial appearance and so forth...the list is virtually endless. The means by which those desired traits were obtained was to selectively breed that population of dogs that most strongly exhibited the desired trait; a breeding strategy that is otherwise known as inbreeding!

Gene Pool And Population Factors

A population may be described as a breeding group that possesses gene continuity from one generation to the next. Currently a growing body of dog experts believe that the dog evolved as a new species from the wolf to occupy a developing niche about 15,000 years ago. That developing niche revolved around human waste dumps; opportunistic wolves began inhabiting those waste dumps for easily available food supplies.

All told, 15,000 years on the evolutionary scale is an extremely brief period for a new species to evolve from another, suggesting that there must have been a considerable amount of inbreeding amongst those opportunistic waste-dump-frequenting wolves to propagate the tameness trait in so short a time span! Compounding this issue of limited genetic pool, a growing number of dog researchers now believe that the original genetic ancestry of the dog evolved from only three female wolves that inhabited China several thousand years ago (the so called eves of dog evolution).

The important point to note here is that even before mankind began his intensive trait-specific breeding program of the dog, and due to its unorthodox super-accelerated evolution, the dog gene pool right from the get go was rather limited!

Development Of A Dog Breed

By its very nature the development of a new dog breed involves a considerable amount of inbreeding to magnify and evolve the desired trait(s) characteristic of that new breed. However this process results in a considerable number of undesired results. If we consider the Dalmatian, a breed of dog characterized by its distinctive pattern of spots, somewhere along the line during that process of selecting for the spotted pattern trait, Dalmatian dog breeders unknowingly and unintentionally also bred this dog for an abnormal uric acid gene!

By the time people realized that there was a very serious problem in the Dalmatian, this dog breed was homozygous for the abnormal uric acid gene! (Homozygous refers to identical pairs of genes that manifest as an observable trait as opposed to non-identical gene pairs known as heterozygous that confer no observable trait; i.e., recessives). This unwanted side effect means that Dalmatians are perhaps the only breed of dog that is predisposed to urine stones (from excessive levels of uric acid), a debilitating urinary tract condition. In an effort to rectify this problem the Dalmatian line was subsequently crossbred with various Pointer breeds to eliminate the inherent homozygotic uric acid gene whilst still maintaining the spotted pattern that defines the Dalmatian dog.

Gene Linkage

The abnormal elevated levels of uric acid in the Dalmatian associated with the spotting-pattern gene, is a classic case of gene linkage. Linkage is said to occur when genes expressing different properties are located on the same chromosome and are inherited as a unit. In fact the occurrence of gene linkage probably explains how the dog morphologically (shape wise) differentiated from the wolf so dramatically and so quickly; the gene that expressed the tameness trait was linked to genes that expressed other properties such as floppy ears, change in coat color, barking or simply put properties characteristic of today's domesticated dog.

The bottom line here is that selective breeding for a particular trait (as happens whenever a new dog breed is being developed) carries the inherent risk of magnifying the expression of unwanted defective genes that would otherwise rarely occur under natural circumstances.

Genetic Diversity

During the process of natural selection genetic diversity is maintained, but contrastingly in selective breeding the opposite holds true; genetic diversity is reduced! Recent studies have revealed that genetic variation occurs frequently in normal populations of any species and that even those genes that are deleterious and defective are preserved in the gene pool as so-called recessive genes (recessive gene traits are not visibly apparent unlike dominant genes). It is now believed that such genetic variability confers adaptive properties to a population in the event of extreme environmental change.

Thus mutative genes that confer minimal benefit today could play a significant future role in the survival of the species in which it occurs. This could explain why defective or mutative genes are preserved as recessive genes in a population's gene pool. A good example illustrating the beneficial role recessive genes can confer to a population is the case of the English Peppered moth.

Like a large number of insects the Peppered moth relies on its color to camouflage it from predators. The dominantly prevalent grayish color of the Peppered moth allows it to blend in with its environment which so happen to be tree trunks and lichen of like color. Although lighter and darker shades of the moth exist, few of such individuals survive for the simple reason their camouflaging abilities are less effective.

However with the advent of the industrial revolution in the late 19th century the resultant pollution darkened the tree trunks such that the minority recessive trait which conferred a darker shade of gray to the moths became dominant because such moths were then better able to avoid predation. As pollution levels subsequently decreased the tree trunks gradually reverted to their normal color and so also did the color of the Peppered moth revert back to its pre-industrialization gray. Thus once again the recessive dark-gray color in the moth reverted to its usual minority role!

Combating Dog Genetic Disease

Because almost every single dog possesses at least 4 defective genes (no matter whether it's a purebred or mixed breed) unless strong active measures are taken the problem of dog genetic disease can only get worse. Such strong effective measures by necessity require the participation of everyday dog owners and not just dog breeders or dog researchers!

Dog Genome Project Wants Your Dog's Blood!

The Canine Genome Sequencing Project (Dog Genome Project based at the Broad Institute of Harvard and MIT in Boston) has sequenced the dog genome in its entirety. One of their priority goals now is to identify the genes responsible for causing dog genetic diseases, defective genes, carrier states of hereditary disease and much more. Through using the powerful resource of the sequenced dog genome, the good folks at the Dog Genome Project hope to reverse the widespread prevalence of genetic disease in dogs worldwide.

However to achieve that noble goal they need your help! How?

Well the only means by which recessive genes and carrier states can be identified is at the genetic level (genotype) and not by visual observation of recognizable morphological traits (phenotype). To do this the Dog Genome Project staff need a large number of dog samples to analyze and that is where you, as a dog owner, can play a significant role by sending them a blood sample of your dog.

More about the dog

For more information about how to help alleviate dog genetic disease go to:

http://www.broad.mit.edu/mammals/dog