HCM – Heart disease

HCM – Hypertrophic Cardiomyopathy

What is HCM?  –   Hva er HCM?

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. Hypertrophic Cardiomyopathy means thickening of the heart walls, that make the heart ineffective. The heart can stop, or the cat can get blood clots and die.

If discovered, there is medication and treatment. Also it is good if the cat is not overweight. Some cases of HCM can give sudden death, while some cats can live long in spite of HCM diagnosis. Fox 2018 indicates the following numbers:

  • around 6-7 % will die within the first year
  • around 28-30 % will die within ten years
  • 10 % can live to over 9-15 years age

 

HCM er en hjertesykdom som fins hos alle katter, også vanlige huskatter. Det er den vanligste hjertelidelsen hos katt. Hypertrofisk kardimyopati betyr at hjerteveggene fortykkes, og gjør hjertet lite effektivt. Hjertet kan da stoppe, eller katten kan utvikle blodpropp.

Om HCM oppdages fins det medisiner og behandling. Det er også best om katten ikke er overvektig. Noen tilfeller av HCM gir brå død, mens andre varianter utvikler seg veldig sakte. Noen katter kan leve lenge tross diagnosen. Fox 2018 anslår de følgende tallene:

  • omkring 6-7 % dør det første året
  • omkring 28-30 % vil dø innen ti år etter sykdommen starter
  • 10 % kan leve til over 9-15 år alder

 

HCM in Maine Coon

In Maine Coons, a related colony of cats affected with HCM was studied to discover more about this illness (Meurs 2006), and there has been more research in our breed than other breeds. This does not mean HCM is only found in Maine Coons, but we know a lot more about it than for other breeds at risk.

  • Approximately 10 % of Maine Coon (2018 numbers) 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

 

What to do – Hva bør man gjøre?

Breeders should follow the rules of the PawPeds health programme for HCM, with regular screenings of breeding cats. No one can claim “HCM free” lines, but all breeders can do their best to limit this disorder.

Alle oppdrettere bør følge PawPeds helseprogram for HCM, med jevnlige undersøkelser av avlskatter. Ingen oppdrettere kan påstå å ha “HCM-frie” linjer, men alle oppdretter kan gjøre sitt beste for å begrense forekomst av denne lidelsen.

HCM health programme – DNA testing and echocardigraphy

Both ultrasound screenings and known DNA-status for A31P is necessary for breeding cats.

We scan (ultrasound) our breeding animals according to the PawPeds health programme, with scans by a veterinary specialist, see list of PawPeds approved veterinary cardiologists. All results from these scans are publically available in the PawPeds Maine Coon database.

All our cats are negative for the HCM1-A31P DNA mutation.

 

Både ultralyd og DNA-testing er nødvendig for avlskatter.

Vi hjertescanner våre avlskatter etter PawPeds’ helseprogram, med ultralydundersøkelser hos hjertespesialist, se egen liste over PawPeds-godkjente kardiologer. Alle resultater fra disse er offentlig tilgjengelige i PawPeds Maine Coon-database online.

Alle våre katter er negative for A31P-mutasjonen.

 

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 7 years), as most cases of the disease usually develops quite late in life.

Recommendations are ultrasound scans repeatedly through the cat’s life:

  • at 1 year’s age and at least before breeding
  • 2 years age
  • 3 years age
  • 5 years age
  • after 7 years of age, 8-9 is very good

 

For å undersøke katten for klinisk HCM er det nødvendig å utføre ultralyd hos spesialist på hjerte, og denne undersøkelsen må gjentas flere ganger gjennom kattens liv. Det viktigste er først å scanne unge avlskatter før paring, slik at de alvorlige tilfeller med HCM i ung alder kan tas ut av avl. Det er også svært viktig å scanne de middelaldrende og eldre avlskatter (over 7 år), ettersom de fleste tilfeller av sykdommen vanligvis utvikles sent i livet.

Helseprogrammets anbefalinger er gjentatte hjertescanninger gjennom kattens liv:

  • ved 1 års alder og før første paring
  • 2 års alder
  • 3 års alder
  • 5 års alder
  • etter 7 års alder, 8-9 er veldig bra

 

HCM

Illustration from Vetbook.org

A heart ultrasound scan shows the heart’s status at that date and age. It is therefore important to follow the recommendations of continued HCM-ultrasounds, as the cat gets older, and especially at high ages. Some critics claim that a heart scan shows only “a moment in time”, but that means they have not quite understood how HCM works. “Still healthy heart at this age” is a better formulation, and describes also why continued scans are needed, and why they are more valuable the older the cat is.

 

En hjerteultralyd viser hjertets status pr den dato og alder katten har undersøkelsesdagen. Det er derfor viktig med fortsatte HCM-undersøkelser, etter hvert som katten blir eldre, og det viser viktigheten av å undersøke på nytt ved høy alder. Enkelte kritikere påstår at en hjerteultralyd bare er “et øyeblikksbilde”, men det viser at de ikke har forstått hvordan HCM virker. Det er mer korrekt å si “fremdeles friskt hjerte ved denne alder” – og jo eldre katten er, desto viktigere er resultatet.

 

Challenges for the Breeder  – Utfordringer for oppdretteren

HCM is hereditary, but only one cause, mutation is known, and we know there must be other mutations also not yet known.

  • HCM can be “late onset”, meaning no symptoms at all until the cat is 4-5 years old
  • many breeders scan only young cats, under 3 years old
  • HCM scans before breeding and at under 2 years of age, will only discover the “early onset” cases
  • HCM seems to sometimes skip a generation and then reappear in offspring of the next generation
  • most cats who die early will not have autopsies, so cause of death will remain unknown

 

DNA-test: A31P – HCM1

Most Maine Coon breeders test for the one known factor  that can cause HCM, the A31P mutation in the MyBPC3 gene, often called HCM1. 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

 

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. In the future there will hopefully be yet further HCM-mutations discovered to test for. There is ongoing research.

 

Patterns of matings:

It is very important to know A31P (HCM1-DNA) status to avoid homozygous positives who have a very high risk of illness.

 

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

Read my article (review study) 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 – Forskning og studier:

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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