Persian Cats and Hypertrophic Cardiomyopathy (HCM)

Hypertrophic Cardiomyopathy (HCM) is the most common form of heart disease in cats that is characterized by the thickening of the heart muscle. It can result in congestive heart failure, thromboembolism (the blocking of a blood vessel by a particle that has broken away from a blood clot at its site of formation), and occasionally sudden cardiac death.

Symptoms of HCM

Some of the symptoms of HCM include: loss of energy (lethargy), deep chest breathing without exertion, and/or hind leg paralysis (because of a blood clot). At younger ages some cats may have a heart murmur, but not always.

Treatment for HCM

HCM can be treatable with medications and can add months or even years to the life of a cat with HCM. Your veterinarian is the best person to discuss treatment choices and medications.

Is HCM Genetic?

While hypertrophy can occur secondary to certain other diseases in cats, most cases of HCM have no underlying cause and are considered to be a primary disease of the heart itself. The identity of the HCM gene mutations are only in the Maine Coon and Ragdoll breeds. And so far, little is known about Ragdolls.

Genetics 101

Offspring receive a copy of each gene; one from the mother and one from the father. If a mutation occurs in one copy of the gene, it is "heterozygous" and are usually not affected but are considered carriers. If both copies of the mutated gene are present, it is "homozygous".

In Maine Coons, cats that carry one copy of the gene mutation ("heterozygous") usually do not develop HCM when they are young (less than 5 years old). It is unknown what happens to these cats when they get older. There are cats that carry one copy of the mutated gene ("heterozygotes") all of their life and never develop HCM. Others develop mild to moderate HCM, live with it, and never have a problem. However, these heterozygotes cats do pass on the mutation to their offspring. Cats that have two copies of the gene ("homozygotes") usually develop HCM between 6 months and 5 years old.

HCM is believed to be a recessive (homozygous) genetic disease, but there may be an environmental part in developing the disease. In Maine Coons and Ragdolls, the homozygous recessive appears to increase the risk of development of the HCM disease. However, not all cats with the homozygous recessive develop HCM and some cats (in these breeds) do develop HCM but do not have the defective gene.

Click here for an explanation of inheritance probability.

Ultrasound and Genetic Testing for HCM

The University of California, Davis has a DNA (genetic) test for HCM for the Maine Coon and Ragdoll breeds. However, as of the date of this article (January 2014), there is no HCM DNA test for the Persian cat breed. Currently, the only way to test for HCM in Persian cats is by an ultrasound of the heart. If affected, there will be evidence of cardiac enlargement. More often than not, the Atrioventricular Septum (AV Septum - a septum of the heart between the right atrium (RA) and the left ventricle (LV) will enlarge before the heart muscle does. A single normal ultrasound result does not guarantee the cat will remain disease free. Also, some affected cats may not develop detectable changes to their heart on ultrasounds until later in life and some changes may be mild and/or subtle. Currently, recommendations are an ultrasound be done every two years.