Thursday, July 24, 2014

What’s in Your Pedigree: Genetic Screening



                       

For those blog followers who have been clients of mine for almost 30 years, there has never been any question as to the lack of royal lineage in my background. My father hails from a whiskey bootlegging family in Western Kentucky. All gained riches during the Depression were followed by relatives serving jail time.  They made liquor runs from Nashville to Louisville and yonder.
  My Mother was the daughter of an architect and granddaughter of a German Presbyterian minister from New York City. They met at Cornell University where my mother worked in my father’s nutrition lab. The intersection of these 2 cultural background is “yours truly."

My dog, Taco Belle, was found in a trailer park in Zebulon, NC. Looking at her one would say she is a Dachshund/Chihuahua cross. Recovering since last week from a collapse disk at Lumbar vertebrae 1-2, her genetic framework makes her more prone to weakness in her mid- back area. I am happy to report she is improving with rest, pain medications, and strict exercise restriction. In her first year, I had sent out a new genetic screening blood test, advertising the benefits of genetic screening to better treat genetically linked disorders. Taco Belle’s test results stated Bassett Hound x Rhodesian Ridgeback (so much for the early genetic blood testing in 2007). It states the obvious:  test results are only as valid as the accuracy of the test (also called sensitivity and specificity).

Let’s look into some of the current genetic screening tests for pets.

WHAT IS THE BASIS FOR GENETIC SCREENING OF ANIMALS?

With natural selection, the "survival of the fittest," although a buzz word for healthy, truly has a genetic basis. Due to man’s interference, selecting for certain physical traits is reflective of man’s preference, not necessarily for the betterment of the animal. With greater than 120 biochemical/DNA screening tests for defects (and the list is growing), it is confusing for both owners and  veterinarians what are the proper background checks prior to purchase of a specific breed of cat or dog. The confusion is magnified with the new tendency towards “designer breed” crossing. Although touted to bring out the best in both parents, this breeding can increase the tendency of bad traits. For example, when both parents come from a breed known for allergies, the offspring, even though a mixed breed (outcross) may have an increased tendency to allergies as well. Basil D'Gerolamo pictured. 




SO WHAT ARE THE WAYS TO TEST FOR KNOWN DEFECTS?

Once beyond the physical exam, the following are important indicators of disease: physical exams, radiographs, and laboratory testing for genetic markers. 
WHAT IS ONE OF THE biggest fallacies of testing pets?
Many young, breeding stock pets will be examined and pronounced clear (phenotypically) on eye and orthopedic exams of many inherited conditions (via eye exams and radiographs). However many will as adults develop inherited eye and joint problems.



WHAT IS ONE EXAMPLE OF A GOOD SCREENING BLOOD TEST IN CATS?

Persians, Himalayans, and other cats with Persian ancestry should be screen for Polycystic Kidney Disease. It is a progressive, inherited disease that leads to cysts on the kidneys, renal failure, and death. By testing both the queen and tom (both parents) negative for the PKD1 gene prior to breeding, the risk in the kittens is eliminated. The list of breeds carrying this genetic disease is expanding. Otherwise the disease is diagnosed with ultrasound of the kidneys of cats at risk as early as 10 months of age.  In the past, up to 50% or more of Persian cats may have been affected by this disease. Sofi owned by Ian Fletcher pictured



IS THERE A GENERAL WEBSITE TO CHECK FOR GENETIC DISORDERS OF CATS?

WHAT IS ANOTHER EXAMPLE OF A GENETICALLY SCREENED DISEASE?
Hypertrophic cardiomyopathy of Ragdoll and Maine Coon Cats is condition where the heart wall muscle thickens. By reducing the heart chamber size, less blood is pumped with each contraction. Thus it may to heart disease, blood clots, and often sudden death.
WHAT HAS MADE GENETIC TESTING SO MUCH EASIER FOR CAT BREEDERS?
Many tests of today are performed on cheek swab samples, rather than traditional bloodwork.
Betsy Sigmon DVM, Diplomate American Board of Veterinary Practitioners, Canine & Feline

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