Heart Disease - HCM

Heart Disease, (Hypertrophic Cardiomyopathy), is a major cause of deaths in household cats.  This hereditary disorder causes thickening of the heart wall, eventually leading to failure of the heart, fluid in the lungs, or death from blood clots.  Hypertrophic Cardiomyopathy (HCM) has been documented as a hereditary trait in the Siberian breed. It is a devastating illness that can show at any age.

Only one defective gene is needed to cause HCM, though the disease will show at different ages in different cats. Some cats with an HCM gene may die as early as a year of age, while others may live to six or eight years old.

The Siberian breed is relatively young, making research into this disorder much faster than in other breeds.  SRI has performed large studies about Siberian HCM, and has isolated six foundation points where the disease entered the breed.  Currently, there are no genetic tests for the different types of Siberian HCM. 

Siberian Research encourages both pet owners and breeders to cooperate in pedigree and genetic studies that will help reduce the deaths from this disease.

Researchers at U.C. Davis and WSU are both studying the genetics of Siberian HCM, and searching for the specific genes that are causing this disease.  If you have a Siberian that has been diagnosed with HCM, please consider sending echocardiograms and DNA for study.

There is a delicate balance between fact and assumption. This paper reviews what we know to be true and what we are able to infer as high probabilities given our pedigree research into this disease. Note: as more information forward over time, it may change our preliminary conclusions.

In October of 2006, SRI sent our pedigree review of Siberian HCM to Dr Leslie Lyons and Dr. Kathryn Meurs. While DNA studies are ongoing, we will attempt to discuss known facts about Siberian HCM, and make some general assumptions using those facts.

A general understanding of HCM and cattery practices may help understand why the disease seems to appear and disappear over generations. HCM is considered "genetically dominant", "variable expression", and "delayed onset". In layman terms this means:

  1. Only a single gene from one parent is needed for a cat to show symptoms or die from HCM.
  2. The severity and progression of the disease will vary from one cat to another.
  3. The first symptoms may occur at a young age or later in life.

Secondary genes may either suppress symptoms or activate the HCM gene. The presence of these "modifiers" or "helper genes" is one reason HCM seems to disappear or reappear suddenly within a given line.  HCM seldom appears without a genetic component.

Cattery practices vary when it comes to dealing with disease. Some catteries neuter breeding cats that present with heart murmur and may or may not perform echocardiograms. A few catteries have knowingly continued breeding despite HCM deaths in their lines. This is most common where cats demonstrated excellent conformation.

Pedigree analysis of Siberians indicates a minimum of five separate points where HCM may have entered the breed. These cats came from Moscow, St Petersburg, Germany, and the United States.

The highest levels of deaths are reported on lines with heavy inbreeding Several early charts were created illustrating potential lines where the HCM might have traveled. These charts were effective in demonstrating how HCM surfaces in irregular intervals, but they were flawed as different types of Siberian HCM mixed.

St Petersburg and Moscow clubs have older and more extensive pedigrees than are available to the Western world, but the clubs in those cities are reluctant to correct pedigrees or report HCM in their breeding stock. This information would help isolating foundation lines with HCM.

We encourage breeders to study HCM cases and compare their current breed stock with known cases. While some catteries have only a few potential carriers, others are less fortunate. SRI believes in reducing risks of all genetic diseases in the Siberian Breed.

We encourage breeders to compare the pedigrees of their breeding cats against known HCM cases. When purchasing a kitten or cat, it is quite reasonable to request echocardiogram results of the parents, and a warranty against genetic disease.

The following Studies and Links may be out-of-date.

General Description of Feline Hypertrophic Cardiomyopathy:

Special Report to the Winn Feline Foundation:
Feline Hypertrophic Cardiomyopathy: Advice for Breeders 

Feline Hypertrophic Cardiomyopathy (HCM) Testing
This paper discusses how HCM gene tests for Maine Coon and Ragdoll work, and why gene tests and ultrasounds may not always have the same results.

PawPeds - The Siberian Database
This wonderful open-registry database of Siberian pedigrees is a world-wide treasure. Our heartfelt thanks to Eva Gunnarsson for these records. When researching the purchase of a new kitten, we recommend checking the health records of the ancestors.

Gesunde-Rassekatzen (Siberian Health Database)
This German Database with HCM, PKD, and blood group records is maintained by Tina Weiß.

Dr. Meurs discussion at the 2006 Ragdoll Congress
This informative two-hour talk and question/answer session regarding HCM is available on video. When we last checked, you could purchase this DVD for $15, by contacting Linda Kauffman.

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