Recommendation from Jerold S Bell, DVM
Clinical  Associate Professor of Genetics

My normal recommendations concerning genetic counseling and genetic disease management are based on two (sometimes conflicting) premises. One is to prevent more affected individuals  from being produced, and the other is to maintain the quality and diversity of the breed.

With an autosomal dominant disorder with a genetic test, the recommendation is to replace positive testing cats with a normal 1st degree relative (a normal parent, littermate or full-sibling, 
half-sibling, or prior-born offspring). This is based on not wanting to produce more affected cats.

The other variables present with HCM in Maine Coon Cats are; 1) there is more than one genetic cause for HCM, and there is only a test for one form, 2) not all HCM positive testing  cats develop heart failure.

With test results coming back in the 35% to 38% range (including both heterozygotes and homozygous affecteds), and assuming bias that breeders with affected cats are testing more diligently at this time than breeders who do not know that they have positive cats;  it still
conservatively leaves over of the breed carrying this defective gene.

The biggest issue is what breeders will be doing to the Maine  Coon Cat gene pool if they start massive spaying and neutering of breeding stock.  This is only the first testable gene in the breed, and others will come.  If these tests are used only to exclude cats from  breeding, then there will eventually be no more breeding cats left; as all will carry some deleterious genes.

I am attaching an article that I  wrote for the Persian breed with their test for PKD. Your breed is in a similar situation.  I am not a proponent of breeding all HCM  positive cats, but prudence suggests that some high quality affected cats may be bred in the next generation if the family line does not contain quality HCM gene negative cats. This is a single testable gene, and quality breeding lines should be continued to maintain breed diversity.

Please let me know if there is anything else that I can do  to assist you.

Sincerely,

Jerold S Bell, DVM
Clinical  Associate Professor of Genetics
Department of Clinical Sciences
Tufts  Cummings School of Veterinary Medicine
860-749-8348, fax  860-749-4760

Recommendation from Jens Haggstrom, DVM,
PhD, Diplomate ECVIM-CA (Cardiology) Professor Internal Medicine

You Maine Coon breeders are in a good position for eradicating (or at least significantly reduce) the presence of HCM in your breed. However, with the development of the genetic test and the echo screening, some difficult decisions must be made. The work that Drs Meurs and Kittleson have done is, in my opinion, quite extraordinary and they should congratulated for it. They have clearly shown that HCM is associated with one form of HCM in your breed. However, we know that cats, in general, probably have more than one mutation causing HCM (because cats with known HCM have been shown to be negative for the mutation). It may even be so that more than one gene cause HCM in Maine Coons. The value of a negative cMyBP-C test is therefore limited to rule out HCM. Therefore, it is my (and others) opinion that the test cannot replace echo screening. On the other hand, it appears that cats found normal on echo can have the mutation, a finding that is agreement with what has been found in people with HCM. Thus, the tests are not interchangable, but compliment each other.

It is currently not fully evaluated what happens to those who have the mutation, but have not yet developed echo changes at a particular age. This is an area that I know several researchers are interested in at the moment, and this can only be answered by prospective cohort studies.  I guess that all realize the value of the test, but what may be confusing is how to make best use of this information. The most dramatic measure would be to neuter all with the mutation. If the prevalence of 30% of the cats is true for the general population, that would mean a dramatic reduction of number of available breeding cats. I am not a population geneticist, but from what I have heard of similar situations in dog breeding, it is not advisable to exclude such a big proportion of breeding animals for one cause. There is always a potential danger that other bad genes (causing other disease) can emerge when a population passes through a "bottleneck". I guess all agree at the moment that it is not correct to breed those with the mutation without control of how it is transferred over to the offspring. So, if cats with the mutation are used for breeding two things must be realized, which are 1. Offspring carriers are at risk for developing manifest HCM and clinical signs of disease (although we do not completely know the exact risk) 2. Significant testing is required to have control of cats with and without the mutation in the offspring. Furthermore, cats with the mutation should preferably be mated with those without, but breeding should preferably be done on offspring without the mutation. I guess it all comes down to personal philosophy, and my choice would be to go the more gentler way and try to avoid breeding cats with the mutation, but when this cannot be realized, there should be control of the spread to the offspring.

Best regards,


Jens Haggstrom, DVM, PhD, Diplomate ECVIM-CA (Cardiology)
Professor Internal Medicine
Faculty of Veterinary Medicine and Animal Science
The Swedish University of Agricultural Sciences
Jens.Haggstrom.@Kirmed.slu.se

 

 

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