Cardiomyopathy can occur in all cats, but is most common in breeds such as Maine Coon, Ragdoll, Sphynx, British Shortair, Siberian
Pathology may occur in primary or secondary form.
- Pathology in primary form is hereditary, from the clinical and echocardiographic point of view it manifests mainly after reaching sexual maturity.
- The secondary form is a consequence of other pathologies, such as: hypertension, hyperthyroidism, renal failure.
In order to prevent reproduction of sick individuals, the most interesting for breeders is pathology in its primary form.
Genetically determined disorder developing as a result of mutation, i.e. abnormalities in genes responsible for the production of myocardial proteins. Hypertrophic cardiomyopathy is characterized by autosomal dominant inheritance.
The mutated gene encodes a protein called Myosin Binding Protein C3 (replacement of one of the amino acids in the protein encoding sequence called Myosin Binding Protein C – MyBPC3) and allows to determine whether the cat is a heterozygote (i.e. has one defective and one correct allele from the pair forming the gene) or a homozygote (either both alleles are correct or incorrect). Under normal conditions, Myosin Binding Protein C3 is intended to help the actin and myocardial muscle fibres to be arranged in an orderly and parallel manner, and when a mutation occurs the fibres are usually placed diagonally and/or perpendicularly. As microscopic studies have shown, heterogeneously overgrown muscle fibres are disordered over vast areas and chaotically arranged in different directions. This disorder is probably one of the causes of abnormal diastolic stiffness and arrhythmia observed in hypertrophic cardiomyopathy.
This mutation was described in Maine Coon and Ragdoll cats, the breeds in which the mutant gene was studied. There is also a genetic test to determine it.
The test detects only one mutation (replacement of one of the amino acids in the protein coding sequence called Myosin Binding Protein C – MyBPC3) and allows to determine whether the cat is a heterozygote (i.e. has one defective and one correct allele from the pair forming the gene) or a homozygote (either both alleles are correct or incorrect).
For other breeds, this laboratory possibility still does not exist.
A gene that mutates is called P (positive), if it does not mutate is called N (negative).
Therefore, homozygous PPs are cats that should be excluded from breeding, whereas heterozygous NPs rarely develop this pathology before 3-5 years of age (but there are difficulties in late monitoring of these individuals and it is likely that biological and environmental factors affect the development of HCM).
This suggests that NN individuals should be free of the pathology, but in fact it has been shown that they can develop it.
The reason can be explained by the fact that cats’ HCM can be caused by a mutation of many genes, as in the case of hypertrophic cardiomyopathy in humans. It was shown that this pathology can be determined by a mutation of about 10 different genes.