HCM – Heart disease

HCM – Hypertrophic Cardiomyopathy

HCM is a heart disease that can be found in all cats, also housecats, and it is in fact the most common heart problem in cats. In Maine Coons, a related colony of cats affected with HCM was studied to discover more about this illness, and there has been more research in our breed than other breeds. This does not mean that there is more HCM in Maine Coons than other cats, but we know a lot more about it.

  • Approximately 25-40 % of Maine Coon carry a mutation that increases risk of getting HCM
  • Approximately 5-15 % of Maine Coons will develop HCM during their life
  • Offspring of tested lines have much lower risk than offspring of non-tested lines

 

HCM health programme – DNA testing and echocardigraphy

DNA

Most Maine Coon breeders test for the main factor that can cause HCM, the A31P mutation in the MyBPC3 gene. This genetic test is only one indication of risk of getting ill with HCM later in life, but it seems to be responsible for many of the cases. Cats who have “double” of the affected gene (homozygous positive) have a very high risk of getting ill, and a slightly higher risk is also seen in those with one gene (heterozygous positive), but these cats will typically stay healthy until at least 4-5 years old and those who get ill might not be as seriously affected (Longeri 2013).

  • N/N: normal risk (around 5 %)
  • N/A31P HCM: almost 2 times risk
  • A31P HCM/A31P HCM: around 18 times risk

However there are cats who suffer from HCM who are N/N (negative) for the MyBPC3 A31P gene, implying that there must be other yet undiscovered factors involved.

Ultrasound – echocardiography

To check for HCM it is necessary to scan for clinical HCM through ultrasound (echocardiography), and this test needs to be repeated several times in a cat’s life. The most important is to first scan young breeding cats before they are mated the first time, in order to leave the most serious cases who get HCM early out of breeding. Then also very important is to scan middle aged or older breeding cats (over 8 years), as the disease usually develops quite late in life.

We scan (ultrasound) our breeding animals according to the PawPeds health programme. Their recommendations are ultrasound scans at 1, 2, 3, 5 and 8 years of age, always by a veterinary cardiologist with special training, see list.

HCM

Illustration from Vetbook.org

Patterns of matings:

It is very important to know A31P status to avoid homozygous positives who have a very high risk of illness.

 

Overview of all the research done on A31P and HCM in Maine Coons

Read my article on HCM/A31P in MCO and research:

Berge. 2014. “A31P DNA-test and HCM in Maine Coon.

Berge. 2014. “A31P DNA-test og HCM-sykdom hos Maine Coon

List of reference papers with links to full text under Research papers below.

Excerpt with findings

Comparing the numbers from all the research studies (table 2), a more complete picture can be seen. The number of cats in a study, the gene frequency of A31P for those cats, and the number of affected cats can all influence the results of a single study.

Wess who concluded that A31P had no effect on HCM, also had the smallest study, and the gene frequency for A31P in his study was significantly lower in his study than in all the other studies. The number of cats diagnosed with HCM was also higher than the supposed prevalence for HCM in the breed. This could have influenced the conclusion. Longeri who also did a meta study based on Longeri, Mary and Wess arrived at similar numbers that we see in table 2 regarding disease prevalence and gene frequency.

HCM tab2

Summed up these studies show:

  • Homozygous cats have a highly increased risk to get HCM, with few cats without signs of illness at 4-5 years of age.
  • Heterozygous cats also have an increased risk, but the disease strikes much later and often after 5-8 years of age. Over half of the cats are healthy at 5 years of age.
  • A high number of the HCM-affected Maine Coons do have this mutation.

 

Summary and Conclusion

Summing up the results of all the studies, it is clear that there is a strong correlation between the A31P mutation and development of HCM. It is also clear that HCM is found among cats without this mutation, so there are other causes in addition to A31P.

Both DNA-testing with a gradual selection away from the mutaton from the gene pool, and repeated ultrasound scans (echocardiography) by a cardiologist are necessary to limit the cases of HCM in the Maine Coon breed.

 

Research papers on HCM

HCM and the A31P mutation in Maine Coon

 

Other HCM research

 

Resources

 

I happen to feel that the degree of a person’s intelligence is directly reflected by the number of conflicting attitudes she can bring to bear on the same topic.

  –  Lisa Alther

 

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