Over the past 18 months the study’s investigators have screened 162 Birmans for heart disease. They found a high prevalence of cardiomyopathy (heart muscle disease) in Birman cats (10%). Birman cats seem to be affected by several different types of cardiomyopathy, such as hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC). However, HCM was the most common type of cardiomyopathy in their population, affecting nearly 7% of the Birman cats that they screened. This type of cardiomyopathy causes thickening of the walls of the heart.
HCM was most commonly diagnosed in adult cats (median age of 8.4 years), as previously described in other feline HCM studies. This means that cats may develop HCM later in life and a normal heart scan at a young age does not exclude the possibility of a cat developing HCM at a later stage. Serial heart scans and exclusion of HCM in previous generations is required to properly exclude this disease.
Heart murmurs appear to be more common in Birmans with cardiomyopathy (heart muscle disease) than in healthy cats. Although heart murmurs are not always a reliable indication of heart disease in other breeds, the investigators findings suggest that any Birman cat with a heart murmur should be investigated further for heart disease with echocardiography.
In cases of HCM, the septal wall of the heart was most commonly thickened, which is typical of humans with inherited HCM. Males were more frequently affected with HCM in their study population (82% of the HCM cats were male), as repeatedly shown in feline and human HCM studies.
Eleven Birmans that died of heart disease were submitted for pathological analysis, and similarly to the heart scan results they found evidence of different forms of cardiomyopathy, including HCM, RCM, ARVC and dilated cardiomyopathy (DCM). In humans, these types of cardiomyopathy are usually associated with different genetic mutations, but occasionally one genetic mutation can cause multiple types of disease. They have identified families of Birmans that include cats with HCM and RCM, and cats with HCM and ARVC. It is possible that there is more than one mutation in these families, but it is also possible that one mutation in a Birman family can result in different types of cardiomyopathy.
The investigators have also investigated blood tests that can help identify cats with heart disease (cardiac ‘biomarkers’). Levels of these cardiac biomarkers are increased in the bloodstream when the heart chamber walls are under strain (shown by the biomarker ‘NT-proBNP’) or when heart muscle cells are damaged (shown by the biomarker ‘troponin-I’). These biomarkers do not appear to be helpful in all breeds when screening for cardiomyopathy, but they do appear to be helpful in Birmans. As there is an overlap in biomarker levels between healthy and affected cats, biomarkers will not be reliable enough to act as the sole test in screening breeding cats. Biomarkers may be useful however in determining which cats should be investigated further with echocardiography. Early diagnosis of more severely affected cats will allow cats to be started on treatment to reduce the risk of blood clots (‘aortic thromboembolism’), which is a devastating and often fatal complication of cardiomyopathy.
They have built a large bank of stored samples for DNA from screened Birmans and Birmans with severe heart disease. This will allow them to proceed to the next stage of their studies, where they will look for genetic differences in Birmans with cardiomyopathy compared with healthy Birmans. Their hope is that by identifying genetic differences it may be possible to produce a gene test for cardiomyopathy in Birmans.
Reference: Phenotypic characterization of cardiomyopathy in Birman cats. (Winn Funded Study), final progress report
Principal Investigator, Professor Virginia Luis Fuentes, University of London, Royal Veterinary College
