Cat Breeds Which Are More Likely to Suffer From Hypertrophic Cardiomyopathy (HCM)
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Cat Breeds Which Are More Likely to Suffer From Hypertrophic Cardiomyopathy (HCM)

Hypertrophic cardiomyopathy (HCM) is a heart problem characterised by thickening of the heart muscle. This reduces the size of the chambers of the heart, and therefore reduces the volume of blood that the heart can pump with each contraction. HCM is the most common form of heart disease in cats and can cause heart failure, thromboembolism (obstruction of a blood vessel by a blood clot), and occasionally sudden death in cats.

HCM can occur in cats of any breed, and also in non-pedigrees. It can also occur secondarily to other conditions, such as hyperthyroidism. However, it is now thought that genetic factors account for the majority of cases of HCM. This means that some cat breeds are more likely to be affected than others. Let us take a look at what breeds are likely to suffer from this condition.

Breeds Most Likely to Suffer from HCM – Maine Coon and Ragdoll

Genetic mutations predisposing to HCM have been identified in both the Maine Coon and Ragdoll. Research has shown that up to a third of all Maine Coons and Ragdolls may be carrying the abnormal gene, and thus be likely to pass on the disease to their offspring, even if they are not affected themselves. Interestingly, a different mutation is found in each breed. It appears that the presence of the defective gene increases the risk of a cat developing HCM, but does not guarantee it. Genes are inherited in pairs, and if a cat is homozygous for the mutation ( ie has two defective genes) this increases the risk of HCM compared with a heterozygous cat, ie one which has just one defective gene and one normal gene. However, the relationship between the presence of the mutated gene and the development of HCM is not perfect. The gene defect appears to increase the risk of disease, but not all cats with the defect develop HCM, and some cats in these breeds that develop HCM do not have these defects. It is likely that other as yet unidentified gene defects and other environmental and biological factors all influence the development of HCM.

Other Breeds Which May be Likely to Suffer From HCM

There are some indications that other breeds may also carry a defect which could lead to HCM, but the situation is complicated, and not everyone agrees. There is ongoing work looking for similar issues in the Norwegian Forest Cat and the Sphynx. Some sources claim that a mutation leading to HCM has been discovered in the American Shorthair. British Shorthairs, Devon Rexes, and Bengals have also been said by some to suffer from this disease, and at least one Persian breeder has claimed that it is more common in Persians than other cats. In the case of the Bengal, the cause has been attributed to the narrow gene pool of these cats. Ongoing research tends to concentrate on any breed in which a higher prevalence of HCM has been reported or suggested. But except in the case of the Maine Coon and Ragdoll, definite evidence is sparse, so reports should be treated with caution. Undoubtedly, other mutations responsible for HCM in cats do remain to be discovered. However, since few veterinary cardiologists and geneticists have the expertise to study genes, it may be some time before the responsible gene or genes for each affected breed will be found. The mutations identified as the causes of HCM in Maine Coons and Ragdolls may not be the same mutations, or even on the same gene, in other breeds. The genetics of HCM in each breed will require detailed investigation of each individual breed, and this may take some time.

Testing for HCM

So what can be done at present? Cats can be tested for HCM in two ways. The traditional method is for a vet to carry out an examination of the adult cat to test for early signs of the disease itself. But a simpler and more reliable technique, now frequently used in Maine Coons and Ragdolls, is by means of a blood or cheek smear test, to check for a specific abnormality in the cat's DNA. Cats which are carrying two genes for HCM should not be used for breeding and are likely to develop the disease. Those which only have one copy of the gene are carriers, and should only be bred from when there is very good reason to do so, and then only with stock which is known to be clear of HCM.

All reputable breeders of Ragdolls and Maine Coons now test for HCM and do their best to completely eradicate it from their breeding programmes. In some countries, registers of breeding cats have been established, so that the genetic status of breeding stock is recorded along with results of ultrasound scanning by a veterinary cardiologist. This information then allows more careful selection of suitable breeding cats. In the UK, one such scheme is operated by the Veterinary Cardiovascular Society, with support from International Cat Care. Cats registered under this scheme can be seen on the International Cat Care website. As can be seen, it is not only Maine Coon and Ragdoll breeders who are testing their cats. Results from other suspect breeds such as the Sphynx, Norwegian Forest, and Bengal are found here, as well as some from breeders of other types of cat.

Conclusion

Of course, all of the above is most relevant to those of us who own Maine Coons and Ragdolls, and also possibly to those who own some of the other breeds mentioned. It is also very important for anyone who is planning to obtain a kitten of one of these breeds. As stated, all reputable breeders now test their breeding cats for the HCM gene. Nevertheless, it is worth checking, particularly before buying a Maine Coon or Ragdoll, that your breeder is one of those who has done so. You want your new kitten to have a long and healthy life, not to run the risk of suffering from a nasty condition like HCM.

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