La cardiomyopathie hypertrophique

Hypertrophic cardiomyopathy is a heart disease that affects the heart muscle, called
myocardium. It is characterized by a more or less significant thickening of the latter, located
mainly in the left ventricle and in particular the interventricular septum
(the hypertrophy of the pillars, the fleshy columns, the free wall of the left ventricle may exist to
a degree variable).

This is not a disease specific to the Maine Coon breed. It affects many animal species
(race or not), as well as humans.

This thickening of the myocardium progressively leads to an alteration of the cardiac function:

– with appearance of disorders of the rhythm (fibrillations, extrasystoles, block of branch …), breaths with
auscultation, dyspnea of ​​effort etc …
– with appearance of complications with pulmonary edema type, heart failure,
arterial thromboses and sudden death.

This pathology often evolves with low noise, with symptoms not visible to the naked eye before
the installation of the first complications.

Transmission mode :

HCM is a genetic disease whose mode of transmission from one generation to another is not
yet clearly defined.
It is the consequence of the occurrence of abnormalities (mutations) on the chromosomes responsible for the
manufacture of the various proteins constituting the heart muscle. In Maine Coon, a mutation
on the MYBPC3 gene coding for myosomal binding protein C (a protein
component of the myocardium) has been identified.
Transmission of the mutated gene is autosomal dominant, variable in expression, and
fully penetrating in adulthood.

– autosomal = mutation carried on an autosome chromosome as opposed to the
sex chromosome . The transmission is therefore independent of the parents’ sex and can be transmitted by
both males and females.

– dominant = only one parent carrying the sick gene is sufficient to transmit it to part of his
offspring.

– variable expression = means that the age of onset and evolution of the disease varies from one
individual to another, even within the same line. Some animals will be seriously affected and
quickly (before the age of 1 year), others will be more discreetly affected and more or less late,
finally some will not seem affected. All will transmit the mutated gene and therefore the risk of expressing
the disease.

– full penetrance to adulthood = means that all individuals carrying the mutated gene will
likely develop HCM at some point in their life, once in adulthood, despite
the variability of expression of the disease.

The identification of this mutation on the MYBPC3 gene led to the development of a DNA test by the
laboratories. The hypertrophic cardiomyopathy triggered by this mutation was labeled TYPE
1 (HCM 1).

In the case of a negative result in the DNA test, ie homozygous healthy for HCM 1, it is not excluded that
no other mutation, currently unlabeled, leads to the development of an HCM
(in Man, more than 220 mutations known on several genes lead to clinical symptoms
of HCM, variable prognosis).

Monitoring and screening:

It is therefore necessary, in the current state of knowledge, to continue the
cardiac ultrasound screening of our Maine coons, since the only DNA test is not enough to rule out the risk of
developing an HCM in our cats.
This examination, performed by a specialist in cardiology and ultrasound, allows the diagnosis of HCM, at a
given time, by visualizing the anatomical and physiological changes of the heart.
It is therefore a tool for detecting the disease. It does not guarantee that the myocardium will be healthy in the
months and years to come. Hence the terrible feeling of Damocles’ sword hanging above the head
for all breeders testing their breeders ultrasographically, waiting for each result.
This review therefore warns of the installation of an HCM, but does not prevent the appearance or
determine the causes.

In breeding, regular ultrasound monitoring of breeders (and ideally retired cats),
every year and before each breeding, seems to me essential, to continue to study the
status of the lines with which we work and to allow the detected cats Positive HCM on
ultrasound to be medically supported to allow them to live as
comfortably as possible with their disease and also make possible further research
on this disease.
Recommendations and follow-up protocols for HCM have been proposed, including by  Pawpeds

Some breeders also ask for an ultrasound follow-up, « adapted », of their kittens placed in
company. This is to have a return on the evolution, heart health, of these kittens not
intended for reproduction. This allows the breeder to broaden his follow-up on his lines, the different
marriages performed and thus have a certain perspective on the work done.

 

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