Hypertrophic Cardiomyopathy or HCM is the most commonly diagnosed cardiac disease in cats. It is estimated to affect 1 in 7 cats. One UK study (see the EveryCat webinar) of shelters, found 1 out of 3 cats over 9 had some degree of HCM. Oftentimes, there is no outward signs until the cat goes into congestive heart failure. Additional complications include clots and “saddle thrombus”.
HCM presents in virtually the same way in cats as it does in humans. It causes a thickening of the heart wall, often the left ventricle. This thickening causes the heart to work harder and harder.
The challenges with HCM is that it is often undiagnosed and subclinical. Even of those with an identified gene, there are complex factors such as incomplete penetrance and potential other mitigating genetic factors that keep the disease from presenting in a severe form or even from presenting at all. This is why you can see HCM offspring from parents who are seemingly healthy. It is also a disease that often presents long after the cats breeding career is over and well into middle or advanced age.
HCM is caused by a variety of genetic mutations, but also affected by epigentic and environmental factors (e.g. obesity, diet, etc.).
There are currently only 4 identified mutations in cats and only 2 genetic tests which are only valid for causation in Maine Coons and Ragdolls. This is compared to over 1400 mutations in humans over 60 different genes. It is likely there are many yet to be identified mutations for cats in general and others in Siberians specifically.
Because of the complex nature of the disease and the pervasive nature of HCM in cats it is unlikely HCM will ever be eliminated. As breeders, we can only do our best to keep track of the health of our kittens, cardiac screen our breeding cats even after they’ve been retired, and use predictive tools like DNA if/when they become available. Even doing all of that and eliminating affected cats from breeding and their close relatives it is still possible to have HCM in a breeding program. The best way to help the breed is to be open about testing results whether good or bad, and incidences of HCM. This is really the only way to reduce the effects within the breed.
In addition, as breeders it is important to educate our pet owners on the importance of an appropriate diet and the importance of maintaining a healthy weight. Obesity in cats can increase the likelihood of many diseases including cardiac disease.