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 ¼ 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