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Introduction

Maine Coons are generally a healthy and strong breed and have evolved to survive the New England climate.  Maine Coons are a slow maturing breed, taking 3 to 5 years to mature. Maine Coons, like all cats (and humans), are affected by Hypertrophic Cardiomyopathy (HCM), the most common heart disease seen in cats (and humans), whether pedigree or nonpedigree. HCM is NOT exclusive to the MAINE COON CAT breed. It has been diagnosed in Ragdolls,Persians and other breeds as well. It is only singled out as APPEARING TO BE prevalent to these breeds, as these breeds have been heavily studied by animal geneticists.  HCM is MORE common in the average feral cat as they can interbreed more rapidly.

“Hypertrophic Cardiomyopathy (HCM) is the most common heart disease of cats whether random bred or pedigreed.” (Kittleson et al)

About 1/4 to 1/3 of apparently healthy cats have a heart murmur. Of these cats,
approximately 50% have heart disease.About 6% of cats don’t have a murmur but
have heart disease. (Christine Duree, DVM)

“Hypertrophic Cardiomyopathy is very common and can affect people of any age. About 1 out of every 500 people have this type of cardiomyopathy.” (ClevelandClinic.org)

About HCM

Hypertrophic cardiomyopathy (HCM) is a condition characterised by the inward thickening of the heart muscle, resulting in a reduction of chamber volume, thereby reducing the volume of blood that the heart can pump with each contraction.  Symptoms include: exercise intolerance, lethargy, difficulty breathing, fainting, and failure to thrive and grow. 

About Heart Murmurs

Murmurs are a common finding and not a symptom. Murmurs are extra heart sounds that are produced as a result of turbulent blood flow which is sufficient to produce audible noise. Murmurs may be present in normal hearts without any heart disease. These types of murmurs, often referred to as innocent or functional murmurs, usually cause no trouble for the individual. The loudness of the murmur reflects the amount of turbulence but is not evidence of severity. The presence or absence of a heart murmur in itself is not indicative of heart disease.  Heart disease can be present in the absence of murmurs.  Innocent or benign murmurs are most common in healthy, young, growing animals and sometimes in adults (related to anxiety, illness, medications, stress, etc) and are therefore clinically insignificant. They can disappear and reappear from one examination to the next.

“A heart murmur is a finding and not a symptom. Babies are thin chested and you can hear the blood moving through the heart due to the rapid growth of the pulmonary arteries. Inside the mother, inside the growing fetus, the pulmonary arteries not getting much blood as mother is supplying the oxygen through the placenta. After birth, when the baby is born, you suddenly have a mismatch between a large central pulmonary trunk and the branches. As the baby grows quickly the output of the heart needs to increase and as the baby is pumping more and more blood through this big trunk and the blood is trying to get to the lungs through these smaller vessles often you’ll get turbulence, and you’ll get a murmur it’s a normal phenomenon you’ll see, a form of functional murmur.” (Source: Michael LaCorte, MD Pediatric Cardiology. Dr. LaCorte served as Chief of Pediatric Cardiology at North Shore University Hospital from 1981-1991 and is presently the Director of Schneider Childrens Center at Brooklyn Medical School: N.Y.U. School of Medicine: Fellowship: Pediatric Cardiology - Childrens Hospital of Boston)

The Causes (Etiologies) of HCM

The causes of cardiomyopathy include infections, toxic causes (drugs, chemical compounds,etc), specific dietary insufficiencies, genetic predisposition, and other unknown causes.  As with most diseases, it is likely that in genetically predisposed individuals, certain environmental triggers will have a great influence on whether HCM will be manifested, when, and to what degree.  With respect to genetics, the mode of inheritance is complex and therefore not clearly understood. 

“This is currently unknown in most cats.” (Kittleson et al)

 “One of the most common primary feline cardiac diseases is idiopathic (unknown) hypertrophic cardiomyopathy (HCM).  HCM is characterized by a massive left ventricular hypertrophy without dilation and is present without any other cardiac or systemic disease.  The secondary form of HCM is usually associated with disease processes such as acromegaly, systemic hypertension, or hyperthyroidism.  The etiology of HCM is usually not known. Multiple etiologies have been proposed including hereditary predisposition, elevation in circulating catecholamines, abnormal myocardial calcium metabolism, abnormal compensatory myocardial hypertrophy due to ischemia and fibrosis, or abnormal primary collagen resulting in secondary ventricular hypertrophy.  Researchers have found evidence that some cases of HCM are inherited in the Maine Coon Cat and the American Shorthair as an autosomal dominant pattern.  Kraus et al identified a litter of five 18 month – old mixed breed cats that all had HCM.” (ADDL – Animal Disease Diagnostic Laboratory, Perdue University, Indiana, USA, 2003)

 Click Here For Document: Idiopathic HCM In The Cat - ADDL - Animal Disease Diagnostic Laboratory, Perdue University, Indiana, USA

“Cardiomyopathy can be acquired or inherited. “Acquired” means you aren’t born with the disease but you develop it due to another disease, condition, or factor. “Inherited” means your parents passed the gene for the disease on to you. In many cases, the cause of cardiomyopathy isn’t known. This is often the case when the disease occurs in children.” (ClevelandClinic.org)

Genetic Testing of HCM

A screening test is now available that will indicate which Maine Coons (and Ragdolls) are carrying this genetic mutation, so they can be identified before they are bred.  Responsible breeders can then use this information to eventually breed this defect out of their colony.

  • Molecular genetic test proves absence or presence of A31P mutation in MYBPC3 gene

A study about HCM in Maine Coon cats was published (this is the first animal model in context of HCM) by K.M. Meurs, et al. A31P mutation in exon 3 of MYBPC3 gene was found in all Maine Coon cats suffered from HCM and was not found in healthy Maine Coon cats even in 100 control samples (Meurs et. al. 2005). Computer analysis showed A31P mutation (G to C substitution in codon 31) modifies myosin binding protein C structure (reducing of alpha helix number and increasing non-specific convolution in protein structure).

MAINE COON HCM GENE TEST RESULTS

Result Codes:

N/N: Negative/Negative: Normal

N/HCMmc: One copy of the A31P mutation is present. Cat is 1.8 times more likely to develop HCM than cats without the mutation.

HCMmc/HCMmc: Two copies of the A31P mutation are present. Cat is 18 times more likely to develop HCM than cats without the mutation.

Another mutation in Maine Coon cats was identified as A74T mutation in exon 3 of MYBPC3 gene. This mutation was introduced in HGM2007 conference by Dr. Nyeberg et al. A74T mutation (G to A) is also known as Koch mutation. Due to non-published scientific data about this gene it is difficult to determine its relevancy to HCM. 

 

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