HCM is the most common heart disease in cats. It can occur in all cats whether random bred or pedigreed. This means a statement that HCM doesn’t occur in a certain breed can never be made.
This also applies to the Russian breed; apart from the fact that this breed is as much at risk of being struck by HCM as any other breed, the Russian is also dealing with added genetic material from, among others, the Siamese and the British Shorthair. These breeds both have known cases of HCM.

The possibility exists, that with the injection of all the good genes these breeds gave to the Russian Blue, to save it from extinction, bad genes, like the ones that can cause HCM, were introduced as well. When the Russian Blue was introduced into the Nebelung breeding program, those genes might have been introduced into that breed as well.
Finally, we also have to consider the possibility of spontaneous gene-mutations taking place, which can account for the spontaneous appearance of HCM in a breed. (Since there are multiple mutations of HCM known, this has happened numerous times already).
Right now, some genes that can cause HCM in the Maine Coon and the Ragdoll have already been identified, but scientists expect to find at least a dozen more mutations for this disease. Currently, multiple studies are being conducted on this.

Heredity
HCM in cats is an hereditary condition, like it is in humans. Studies on a test population, consisting of Maine Coons and American Shorthairs, conducted in the United States by dr. Mark Kittleson and Kathryn Meurs (among others) has shown that HCM is an autosomal dominant trait with a variable expression.
This means the gene is not sex-linked and a cat with HCM needs to have received the gene from only one of its parents.
Next to that, the course of the development of the disease is not fixed; the severity and the timespan within which HCM develops varies from one individual to the next. It is thought that multiple genes play a part in the development of the condition. This also means that a cat can pass HCM on without ever showing any symptoms of the condition itself, and that the age of onset in a parent doesn’t necessarily have to be the same in its offspring.

The symptoms and course of the disease
HCM is a heart muscle disease, in which the papillary muscles and the walls of (mainly) the left ventricle become abnormally thickened. This thickening affects the heart’s ability to flex and decreases the chamber size, which results in a decreased ability to fill and pump out blood. The functioning as well as the strength of the heart is impaired.
The increased stiffness of the left ventricle consequently makes the pressure in the left atrium increase, as it can’t fill with the normal amount of blood from the atrium. This raises the chance of thrombosis and causes an increased pressure in the capillaries of the lungs.
The raised pressure (by blood flowing back) in the capillaries and vessels of the lungs may lead to seepage of vascular fluids into the lungs and the chest cavity.
Cats suffering from HCM will often show signs of respiratory distress, increased respiratory rate, lessened appetite and general lethargy.
One of the most severe complications is the formation of blood clots in the atrium because of slowed bloodflow. When those clots find their way into the circulatory system, they often become lodged where the descending aorta branches to go to the rear legs, resulting in rear leg paralysis (saddle thrombus).
Sometimes signs are nonexistent, the first sign being the sudden death of the cat. The course of HCM may vary a great deal; in Maine Coons for instance the disease is often sudden and severe, resulting in the cat passing away at young age (often two to three years old), while in British Shorthairs the disease may have a very late onset, even past the age of five.
However, most problems occur between the ages of three and five years old, and although HCM occurs in both males and females, males appear to develop the condition at a younger age and die of it younger, too. HCM can be treated – that is, we can make the cat’s life more pleasant – but there is no cure, and death is always the outcome.

Echocardiography
HCM testing may only be carried out by a veterinary radiologist or cardiologist (specialist) who has access to specialized equipment.
Because the disease can develop at any age, a normal echocardiogram is not conclusive evidence that a cat is in fact free of the disease. The cat may develop the disease later on, and pass it to its offspring in the meantime. However, testing is useful in the cases where HCM is diagnosed; we can identify affected cats, refrain from breeding them and start treatment to ensure a better quality of life for the time remaining.
It is recommended to have breeding stock tested around the age of one, before they are started in breeding, and to repeat testing yearly.
It is advised not to test queens while pregnant or nursing, as this could affect the outcome of the test. Preferably “retired” breeding stock will also continue to be tested at a more or less regular basis, to enable timely signaling of possible problems for their offspring.

DNA-testing
Recently DNA-tests have been developed for the Maine Coon and the Ragdoll which have enabled us to track some of the genes that cause HCM in these breeds.
However, those tests are only applicable to the mutations that have been found so far.
Research has already shown that HCM can be caused by different genes, so it is possible that cats that are negative on a DNA-test, still develop HCM as result of the influence of another defective gene or genes.
Up until now, the existing tests have proven ineffective for identification of HCM in other breeds, likely because the HCM in different breeds has different origins.
Further research is currently being conducted.
The SBR-RBF hopes to contribute to this.

The Russian, the Nebelung, HCM and the SBR-RBF
Because HCM can affect any breed, we have to conclude that it can also affect Russians and Nebelungs. HCM has in fact recently been identified in a Russian. Until now, nothing has been done to prevent that this disease will get a hold on our breeds like it has a hold on some others.
Especially if a genetic defect is less common in a breed, breeders are less aware of it, it is often not recognized on time and hardly any research is being done.

This also applies to the Russian and the Nebelung, but the SBR-RBF aims to change this.
Recently the SBR-RBF has signed an agreement with GCS for standardization and certification of HCM tests, in addition to a DNA-database which will be maintained by GCS. This way we hope to contribute to research for other HCM-genes, specifically those that cause the disease in the Russian. This research could eventually result in the development of a DNA-test.
To find out how you can contribute, please read the article “DNA database Russian and Nebelung”

Finally, we would like to stress the importance of yearly testing for HCM by means of echocardiography.

© Stichting Blauwe Rus - Russian Blue Foundation