Bengal hypertrophic cardiomyopathy (HCM)

Bengal hypertrophic cardiomyopathy (HCM)

Bengal cats are not considered to be particularly susceptible to diseases. Unlike the acquired ones, the causes of hereditary illnesses lie in their genes. Even seemingly healthy cats can transmit the disease to their kittens if they carry the adequate genetic defect or mutation. It is important to exclude the sick cats from reproducing without exception and test the young animals for breeding for known hereditary diseases as soon as possible.


Everything there is to know about HCM in Bengal cats:


What is HCM?

Hypertrophic cardiomyopathy represents the enlargement or thickening of the muscular wall of the heart (more precisely of the left ventricle). This disease is hereditary and occurs due to a mutant protein C gene in the structure of sarcomeres (the morphofunctional unit of the striated muscle myofibrils) in the heart muscle fibers.


Why and how HCM occurs?

Genetic mutation is the main cause of HCM. DNA tests on Maine Coon cats have shown that heterozygous cats (have dominant and recessive genes - they have only one copy of the genetic mutation) are less affected than homozygous cats (have dominant or recessive genes - they have two copies of the genetic mutation). This may explain why Bengal cats experience mortality at an early age - they may come from heterozygous parents in which HCM has not been detected by routine testing (echocardiography) when they are young adults (up to 6 years). This gene can have many different mutations, and a DNA test that is developed to detect a single mutation cannot identify all cases of HCM in a particular breed. In other words, a DNA test can give a normal result if it is not specific to the defective gene. Therefore, it is best to test your cat annually!

Also, hypertension and hyperthyroidism, which cause secondary thickening of the left ventricle, are not considered causes of HCM but they can worsen the hypertrophic cardiomyopathy if they occur in a cat with mild to moderate HCM.

Factors that may speed up breathing difficulties or heart failure in a cat with HCM are fever, infection, stress, anesthesia, or intravenous medication.


Breed, sex, and age predisposition

HCM is the most common form of heart disease found in cats around the world, including wild cats. This condition is common in Bengal cats (16.7%), but also in other breeds such as Maine Coon, Ragdoll, or Sphinx. It appears that males (20.4%) are more commonly affected than females (2.1%). Although it occurs at all ages, it is most commonly found in cats between the ages of 5 and 7 years. Once congestive heart failure is reached, the animal can live for 6 to 18 months.


What are the most obvious clinical signs?

With the thickening of the walls of the left ventricle, the heart chamber is reduced, and it can no longer be adequately filled with blood. Then back pressure appears, including in the pulmonary circulation. As a result, pulmonary edema (fluid in the lungs) and/or fluid in the chest cavity will occur. These are manifested by difficult and noisy breathing, with the mouth opened (mouth breathing), gasping, strange body positions such as sticking or placing the chest on different surfaces, stretching the head or projecting the elbows outwards, pale to blue mucous membranes due to the lack of oxygen, decreased appetite, low energy levels/apathy, or the sudden inability to use one or more limbs. If it is not intervened quickly, it can result in the death of your pet.!


HCM diagnosis and risk reduction.

Although there are no DNA tests for Bengal cats for HCM, echocardiography is available. This is recommended to be done annually, being a good way to detect moderately to severely affected felines. In slightly affected cats, cardiac changes may be minimal, and echocardiography may not detect any modifications, which is why annual testing is important.

The disease evolves differently from animal to animal, and cats can die suddenly or live for years. HCM has no cure, but the treatment for chronic heart failure can prevent severe acute heart failure.


What are the recommendations for testing and reproduction?

Testing will be performed annually by echocardiography. This will be done before the female is bred, every time you want to mate her! If, for any reason, you do not want to test your females, test at least the males - they may develop heart changes faster than females. If one of the cats is diagnosed with HCM, it should not be used for breeding and should be reported to The International Bengal Cat Society to be included on their HCM positive cat list. Also, cats that have an equivocal/inconclusive test result (the papillary muscles of the heart are larger than usual or the left ventricular wall is greater than 5 mm) should be removed from breeding and retested at six months or one year.

Positive cats should be neutered or spayed and left to enjoy life as pets (not as breeding animals).

Felines that do not have close relatives who were diagnosed with HCM and have passed the screening test for this disease can be reproduced.

A parent of a cat diagnosed with HCM should only be bred with a cat that has the heart in normal parameters and no close relatives diagnosed with this disease. The same goes for half-brothers and half-sisters of a HCM positive cat. The parents that had at least one HCM positive offspring should never be reproduced together again.

As for the siblings of a positively diagnosed cat, they should be tested until the age of five, and if then the heart is in normal parameters, they can be used for reproduction. The same goes for the offsprings of a HCM positive cat.

The evaluation should always be done by specialists in order to make a correct differential diagnosis between HCM and other diseases that may cause heart modifications, such as kidney failure, diabetes, hyperthyroidism, or hypertension.

An example echocardiography is shown below.

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