Friday 30 July 2021

Five cat breeds that suffer from hypertrophic cardiomyopathy (HCM)

I can quickly think of five cat breeds that are predisposed to suffering from HCM. They are: Maine Coon, Bengal, Ragdoll, Scottish Fold, and American Shorthair. The list is not comprehensive. It doesn't need to be comprehensive for me to question whether purebred cats are more predisposed towards HCM than random read cats. And if they are, why? HCM does affect random read cats and is the most common heart disease and is one of the most common diseases amongst domestic cats.

Ragdolls can inherit HCM
Ragdolls can inherit HCM. Photo: copyright Helmi Flick

You probably know that HCM describes a thickening of the muscles of the heart. The disease is listed as genetically inherited in my books but I also read that the causes are unclear. A study published in the Journal of Veterinary Cardiology titled "The genetic basis of hypertrophic cardiomyopathy in cats and humans", states in the summary that "mutations in genes that encode for muscle sarcomeric proteins have been identified in humans and in breeds of domestic cats with hypertrophic cardiomyopathy.

In people, HCM is a genetic disease. It is a disease of the sarcomere. Sarcomeres are the basic contractile units of muscle and sarcomeric proteins are responsible for the strength, speed and extent of muscle contraction. So, this study is saying that a genetic mutation affects heart muscles, specifically sarcomeres, which causes HCM in both domestic cats and humans.

If it is a genetically inherited disease, I would have thought that no purebred cat would suffer from it because cat breeders could remove carriers of the disease from their breeding lines. That may be an oversimplification. Perhaps the disease is embedded so fundamentally within some cat breeds, going back to foundation cats, that it is impossible to remove this gene from the breeding lines. I just don't know but if that is the case it is surely a failure in the breeding programmes of the purebred cats mentioned in the first paragraph.

Perhaps HCM in these cat breeds and others is the product of selective breeding which is essential to the creation of purebred cats. Cat breeders have to select individual breeding cats that have the correct characteristics in terms of appearance as per the breed standards. Therefore, the breeding stock is reduced in number, which means the cats are inbred. Selective breeding encourages the inheritance of defective genes.

It seems that inherited illnesses such as hypertrophic cardiomyopathy are part of the package when you adopt some purebred cats. They go with the territory. However, I just wonder whether it is possible to change this perception and remove HCM from these popular breeds. I have quite a big page on HCM and Bengal cats which might interest you.

Bengal cats blighted with inherited HCM
Bengal cats blighted with inherited HCM. Photo: copyright Helmi Flick

The Bengal Cat Club (UK club) so that breeders do their best to eliminate HCM from breeding lines. They say that there is very little information about the prevalence of the disease in the various breeds. In other words, how do breeds compare with each other in terms of a predisposition to getting HCM? Perhaps there needs to be more data on that available through a study? 

They say that there are a number of causes but breeders are obviously more concerned with hereditary HCM. As mentioned above, it is caused by a defect in a gene coding for a particular protein in the cardiac muscle cells that make up the heart wall. When the gene is defective the muscle cells are abnormal and they do not contract properly. The heart produces more muscle cells to compensate for this deficiency which results in a thickening of the heart wall.

The upshot is that the ventricles of the heart cannot relax and fill properly, the mitral valve becomes distorted which results in progressive congestive heart failure, the symptoms of which are lethargy and reduced exercise tolerance and an increased respiratory rate.

They say that there is no DNA test at the time that they wrote their article for HCM and Bengal cats. The article is undated. They say that breeders should buy breeding cats from "echo tested lines". This means cats which have been tested with echocardiograms. 

When mating a female cat with a stud cat they say that breeders should use a stud cat who is ideally four years old plus and who has been scanned negative for the disease. It appears that HCM can develop later in life and therefore if you wait you can then detect whether HCM has developed or not. Also, do not sell cats for breeding from young parents as they may develop HCM later. That is another feature of their advice.

All Bengal cats should be screened with echocardiography annually, ideally. It is a very complicated subject from my reading of it. It is difficult to remove the genetic inheritance of HCM from Bengal cats. This probably applies to other cat breeds; the ones mentioned above for example.

It is a great shame that such a wonderful cat as the Bengal is blighted with such a profoundly serious genetically inherited disease. The same sentiment would apply to the other cats mentioned.

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