HCM is the # 1 Killer of Indoor Adult Cats. Although some veterinary and pet health articles provide lists of cat breeds with HCM (hypertrophic cardiomyopathy), even going so far as to state these breed are the only cat affected by HCM, in reality HCM occurs in every single cat breed, including non-pedigreed household pets. In fact, HCM is the #1 killer of any indoor adult cat (an outdoor cat is more likely to die a violent death or from an infection).
Fortunately, HCM in Siberian cats who are not inbred is relatively rare.
Why is inbreeding so dangerous? Inbreeding collects together similar traits. This is beneficial in terms of getting cats to resemble each other ("set type"), but is a negative practice in terms of maintaining the genetic diversity necessary in a healthy breed. When genetic diversity is decreased, the chances of a cat "collecting" a set of disease producing genes is increased.
HCM is a genetic disease that is dominant with incomplete expression. Inbreeding is especially dangerous for a disease like HCM, a disease that is genetic in cause, is dominant (if the cat inherits the gene it has the disease), but is incomplete in expression (the severity and time of expression of the disease varies widely). This leads us to believe that there are co-inherited genes that either mitigate or exaggerate the effects of the HCM gene.
Restricting one's breeding program to maintain consistency in looks reduces genetic vitality. By selecting for certain visual traits for the show wins, and ignoring the need to include genetic diversity in one’s lines, the resultant reduction in genetic variation makes it more likely that any diseases inherited will be expressed, often severely . This is not an issue restricted to one country, or any one breed. Instead, it is related to teh cumulative effects of each individual breeder's practice in selecting healthy, genetically unrelated diverse cats for breeding.
It's more expensive and difficult to breed ethically. Breeders who make this ethical - but more difficult, expensive, and time consuming - choice to select and breed from unrelated or lightly related cats combined with a health testing program designed to remove affected cats from breeding, will produce healthier and better tempered cats. Cats much less likely to have inherited and to die from HCM.
Hypertrophic Cardiomyopathy in Cats
What is Hypertrophic Cardiomyopathy (HCM)?
It is the most common cause of heart disease in cats, and the most frequent cause of spontaneous death in indoor adult cats. In cats with this condition, the walls of the ventricles become thick. However, because the muscle fibers are replaced by fibrous connective tissue (scar tissue), the thicker heart walls do not translate into increased pumping power. In fact, the heart is actually weakened as the affected wall of the heart becomes less elastic and the heart chambers get smaller.
Congestive heart failure occurs frequently in cats with hypertrophic cardiomyopathy. Typically, the left side of the heart is more involved than the right, so the signs of hypertrophic cardiomyopathy are those of left-sided congestive heart failure. Signs of left-sided congestive heart failure are: