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Negative for HCM

22 April, 2008

Good news.

Ananda, my breeding queen, has tested NEGATIVE for the known gene for feline Hypertrophic Cardiomyopathy (“HCM”).

HCM is a disease of the heart.  It causes thickening of the heart walls, weakness, build-up of fluid and eventually, heart failure.  There is no cure for HCM; medication can only slow the progress of this disease.  The anguish of a much-loved pet dying suddenly is something that all responsible breeders want to avoid.  For this reason, any test that can diagnose the possibility of HCM is welcome so that affected cats can be taken out of a breeding programme.

HCM is an inheritable disease, and affects ALL breeds of cats.  However, because studies have been done using Maine Coon cats, there is a tendency to associate HCM with Maine Coons. 

In a study entitled “Familial Hypertrophic Cardiomyopathy in Maine Coon Cats” by Dr. Kittleson, a dominant gene was identified that could lead to the expression of HCM in cats.  Recently, a mutation in the MYBPC gene which is suggested to cause HCM in cats was found by Dr. Kathryn Meurs (Washington State University, USA).

There are a number of testing labs worldwide, but I opted for the Washington State University’s College of Veterinary Medicine HCM genetic testing service.  It costs US$60 per cat.  Registration for the service is done online and offers a choice of testing using either blood samples or cheek swabs.  I opted for cheek swabs, based on the advice of other Maine Coon breeders because it’s apparently something you don’t need special training (aka a vet) to do.

The College sent me the Test Kit, which consists of two cheek swabs.  These are like the mini versions of brushes used to clean baby bottles.  Written instructions were included on how to take the samples.  They were deceptively easy:  each brush had to be inserted on either side of the mouth, between the cheek and gums, and then twirled for about 20-30 seconds to gather the cell samples.  The brushes then had to be air-dried, before being popped into a plastic bag and sent back to the College.

I read the instructions out loud to Ananda, in the hope that she would open her mouth and allow me to insert the brushes and twirl them merrily.

Oooh, the look she gave me.  She was on heat and not looking very cooperative.  On second thoughts, maybe not.

Fortunately, I had a contingency plan.  She was due to go to the vet for a blood test before going to the stud cat.  So I asked the vet if he would take the samples for me.  My vet kindly agreed, and asked his two assistants, to carry out blood test and the DNA sampling.  I gave them the instructions, the twirly brushes and waited.

Much later, the door to the surgery opened, and there stood the two strapping young vets, looking a little hot around the collar.

Apparently the blood test hadn’t been the problem.  But who would have thought that a sweet-natured tortie cat would make a fuss about a few brushes?  After checking to make sure they still had their fingers and toes, the vets handed me the brushes with the samples.

I had the choice of sending the brushes via courier or Royal Mail International Special Delivery.  I called several courier companies and nearly fainted at the cost – the cheapest was about £30!  I was worried that if I didn’t send the samples by courier, the cells would degrade, but a breeder assured me that once air dried, the samples were quite robust.  So I chose Royal Mail in the end, and the samples got there.

The DNA test is not the only means of testing for HCM.  Because there may be more than one gene involved in HCM, another recommendation is to diagnose using an echocardiogram which may show signs of the developing disease.   Echocardiograms only show the state of the heart at a particular point in time, which means that repeated testing is necessary.

The problem with all these tests is that they are inconclusive.  In humans alone, several hundred mutations have been identified that cause HCM.  HCM can develop at any age, and a cat that is normal one year could still have HCM and develop symptoms later in life.  Also, a cat may test positive for the HCM gene, and yet not have any signs in its echocardiogram.

And because the tests are inconclusive, a number of breeders are not convinced that they are absolutely necessary, preferring to breed according to the general longevity and healthiness of bloodlines.  It means that breeders have to put their trust in the honesty of other breeders.  It means that there is an element of the guessing-game if breeding with untested cats.  This perception about not needing to test is slowly changing in the UK, but testing in this country isn’t as widespread as say, in the US or Australia.

There is also, of course, the difficulty amongst breeders in being “open” if a cat tests positive for the gene, in case they get tarred with the HCM brush.  Just to confuse the matter, the HCM gene is variable in its expression – just because a cat tests positive doesn’t mean that it or its offspring will go on to develop HCM. 

More openness, more work, more studies need to be done to address this silent killer.

More links:

For more information on HCM, see: members.aol.com/jchinitz/hcm/index.htm.

And from the same site:  Hypertrophic Cardiomyopathy – The Silent Killer – a tragic story from a Ragdoll breeder about the pain and devastation that can result when cat breeders are not open with one another about any occurrences of HCM in the lineages of their cats.

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