January 25, 2013

The Role of Heredity in Allergies



Having reviewed all this information, I feel chagrined that all this time I was bashing over-vaccination for the health disorders my dog developed; I could have been blaming his breeding. Heredity is a big factor in the development of disease, including allergies.

Although not the exclusive domain of the breed, poodles are predisposed to many diseases.



Health tests permit breeders to screen breeding stock for some of these problems (see CHIC). Moreover, advances in DNA technology are improving the ability to find abnormal genes and develop more tests to help eradicate genetic disease.

Hindsight being 20-20, Matisse was the poster boy for heredity weaknesses.  Based on his health history and symptoms, I am sure he developed two of these and suspect the others emerged in his senior years:
Sebaceous Adenitis Sebaceous adenitis causes the sebaceous glands in a dog’s skin to become inflamed and die. Fortunately, in most cases, it’s a largely cosmetic skin disorder that affects only a handful of dog breeds. The problem usually starts at the head, neck, and back, causing scaly skin and matted, thinning hair as the glands malfunction. There is no cure for sebaceous adenitis, but secondary symptoms, such as yeast infections, must be managed on an ongoing basis, usually with frequent bathing and topical medication. The Standard Poodle is the quintessential sebaceous adenitis patient.

Nasal depigmentation Dudley nose - loss of pigment seen in a number of breeds including the poodle for unknown reasons in which the nose is black when dogs are young but fades to brown or sometimes even white as the dog ages.

Cricopharyngeal achalasia is characterized by inadequate relaxation of the cricopharyngeal muscle, which leads to a relative inability to swallow food or liquids. It is seen primarily as a congenital defect, but is occasionally seen in adult dogs. Repeated attempts to swallow are followed by gagging and regurgitation. Aspiration pneumonia is a common complication. The cause is generally unknown, but may be associated with acquired neuromuscular disorders in adult animals.

Endocardiosis Mitral valve disease is not just a disease of the heart. It’s the disease of the heart for dogs, responsible for a full three-fourths of all canine heart diseases. It’s caused by a degenerative process thought to be genetic. A low-grade heart murmur may be the only early warning sign. Later on, coughing, exercise intolerance, rapid breathing or fainting may develop.
Cataracts A cataract is defined by the Canine Eye Registration Foundation - or CERF - as "a partial or complete opacity of the lens and/or its capsule. In cases where cataracts are complete and affect both eyes, blindness results." Cataracts are among the most common intraocular lesions and a leading cause of vision loss in the dog. Cataracts may be caused by genetics, trauma, ocular inflammation, diabetes mellitus, genetic retinal atrophy, persistent pupillary membranes, persistent hyaloid remnants, specific nutritional deficiencies, congenital abnormalities and uncommonly by other specific metabolic diseases.
Given all the dysfunction possible, I am beginning to feel enormously blessed he was as well as he was for as long as he lived.

So was genetic predisposition his destiny?

According to a clear, simple explanation on Wise Geek
A genetic predisposition is greater genetic likelihood of developing certain things, such as diseases, allergies, temperament, a certain level of intelligence or many other examples.
It is not destiny. Neither human nor dog is assured of developing a disease to which we are predisposed. Environment or other genes that haven’t been identified are also important.
Genetic predisposition is distinct from genes that are always expressed. Those who inherit a gene for Huntington’s disease invariably and ultimately will show signs of the illness. A woman who carries a gene that predisposes breast cancer is at greater risk than women without the gene, but developing the disease is not guaranteed. Some genes, like the one for Huntington’s, really aren’t predispositions and are instead going to work if they have been inherited, no matter what
Here's how I see it.

If you're a rich man's son, you're born on third base. The chances of your accumulating wealth are high. Of course, you can always be a wastrel or ne'er do well; that will depend on your character and initiative. But chances are good, you're also gunna be rich because wealth is in your family.

Same goes for inherited disease.

While predisposition is not destiny, the man or animal who is born with a predisposition to a certain disease has better than average odds that it's going to develop. It is in his family.

As Kimberly Powell writes in an article about How Diseases Are Inherited, this is why breeding is so important.
Many diseases and disorders occur as a result of alterations or mutations in a particular gene; some of these mutations can be passed on to future generations. Sometimes this inheritance is straightforward, while other times additional genetic changes or environmental factors also need to be present for a particular disease to develop.

Autosomal Recessive


Some diseases or traits require two mutated copies of a specific gene in order to develop - one from each parent. Both parents must have the particular gene and pass it on in order for their child to have the disease or trait. If the child receives only one copy of a recessive mutated gene, then they are called carriers; they do not develop the disease, but can pass it on to their children.

Autosomal Dominant

Sometimes, only one parent has to pass on a mutated gene in order for their child to inherit a risk for a specific disease. This does not mean the disease will always develop, but the increased risk for that disease is there.

X-Linked

Many diseases and disorders that are associated with the X chromosome are more likely to be inherited by men than women. This is because females inherit two X chromosomes (one from each of their parents), while males inherit one X chromosome (from their mother) and one Y chromosome (from their father). A man who inherits one copy of a recessive mutated gene on his X chromosome will develop that trait because he has no additional copies of that gene; while a woman would have to inherit the recessive mutation from both parents in order to develop the disease or trait. This type of disorder ultimately affects almost twice as many females as males (although many solely as carriers), however, because an affected father can never pass an X-linked trait to his sons, but does pass it to all of his daughters, while an affected mother passes an X-linked trait to half of her daughters and half of her sons.

Mitochondrial Inheritance

The mitochondria in our cells have their own DNA, which is separate from the rest of the cell's DNA. Sometimes diseases occur when numerous copies of mitochondrial DNA within a cell are impaired or do not work properly. Almost all mitochondrial DNA is carried in the egg, so disease genes carried on mitochondrial DNA can be passed only from mother to child. Thus, this pattern of inheritance is often called maternal inheritance.

An inherited mutation doesn't always mean the disease or disorder will develop. In some cases, a faulty gene will not be expressed unless other environmental factors or changes in other genes are also present. In these cases, the individual has inherited an increased risk for the disease or disorder, but may not ever develop the disease. The inherited form of breast cancer is one such example.
There are a lot of variables with a lot of possible combinations.

So to some extent the role of heredity in developing disease is a genetic lottery. Yer pays yer money and takes yer chances.

That our dog or cat will develop one of the diseases to which it is predisposed is just one of the risks we take when we commit to owning a companion animal. There are many other risks.

Even with the highest fence, the standard poodle of one of my friends was hit by a car when he leapt over it. One of my dog's half siblings had repeated episodes of bloat, an equally deadly predisposition.

Life is predictably unpredictable.

Matisse came from a "good family." His breeder was reputable and highly recommended. I met some other dogs from her kennel around town. They were beautiful and well-mannered. His pedigree was impressive.



He was sired by AM CH Pinafore Prestidigitation, an amazing show dog.




His dam was Safari's Shanghai, dam to many champion show dogs including my dog's siblings.

Both Stella and Celine (Avalon's Power of Love) are show-winning champions who made awesome contributions to the breed standard in terms of temperament and conformation. Even after her own impressive career, Celine alone giving birth to five breed champions.

Online health records suggest that all these wonderful AKC-registered show dogs were health-tested and found to be clear of hip dysplasia, eye disease, sebaceous adenitis at the time of testing.

I rolled the dice.

I guarded against bloat almost constantly. I read every article, list serve and report to recognize the symptoms. I fed him appropriately. In the meantime, heredity, environment and what I did not know that I did not know about preventative care were steadily tipping the balance of his health (homeostasis) toward other disease and stealing away the quality of his life.

He was never healthy again from the first series of puppy shots to the last.

Would I do it again?

There is an enormous frustration, anger and sadness that comes with caring for a dog with allergies and ultimately nursing him through multiple symptom syndromes. At the same time, one's devotion is rewarded with devotion that is unavailable in ordinary animal husbandry and irreplaceable in any other bond except maybe between mother and child.

I gave him the best care possible contingent on the information and resources available to me. He gave my life purpose.

What I know now that I didn't know then, in the case of predisposition to allergies, you don't have to cooperate and you certainly don't have to give it a booster shot.

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