Genotype–phenotype correlation between the cardiac myosin binding protein C mutation A31P and hypertrophic cardiomyopathy in a cohort of Maine Coon cats: a longitudinal study

Hypertrophic cardiomyopathy in purpose-bred cats with the A31P mutation in cardiac myosin binding protein-C

We sought to establish a large animal model of inherited hypertrophic cardiomyopathy (HCM) with sufficient disease severity and early penetrance for identification of novel therapeutic strategies. HCM is the most common inherited cardiac disorder affecting 1 in 250-500 people, yet few therapies for its treatment or prevention are available. A research colony of purpose-bred cats carrying the A31P mutation in MYBPC3 was founded using sperm from a single heterozygous male cat. Cardiac function in four generations was assessed by periodic echocardiography and measurement of blood biomarkers. Results showed that HCM penetrance was age-dependent, and that penetrance occurred earlier and was more severe in successive generations, especially in homozygotes. Homozygosity was also associated with progression from preclinical to clinical disease. A31P homozygous cats represent a heritable model of HCM with early disease penetrance and a severe phenotype necessary for interventional studies aimed at altering disease progression. The occurrence of a more severe phenotype in later generations of cats, and the occasional occurrence of HCM in wildtype cats suggests the presence of at least one gene modifier or a second causal variant in this research colony that exacerbates the HCM phenotype when inherited in combination with the A31P mutation.

Development of a Loop-Mediated Isothermal Amplification Assay Coupled With a Lateral Flow Dipstick Test for Detection of Myosin Binding Protein C3 A31P Mutation in Maine Coon Cats

Background

Myosin-binding protein C3 A31P (MYBPC3-A31P) missense mutation is a genetic deviation associated with the development of hypertrophic cardiomyopathy (HCM) in Maine Coon cats. The standard detection of the MYBPC3-A31P mutation is complicated, time-consuming, and expensive. Currently, there has been a focus on the speed and reliability of diagnostic tools. Therefore, this study aimed to develop a loop-mediated isothermal amplification assay (LAMP) coupled with a lateral flow dipstick (LFD) test to detect MYBPC3-A31P mutations in Maine Coon cats.

Materials and Methods

Fifty-five Maine Coon cats were enrolled in this study, and blood samples were collected. MYBPC3-A31P was genotyped by DNA sequencing. Primers for LAMP with a LFD test were designed. The optimal conditions were determined, including temperature and time to completion for the reaction. The sensitivity of A31P-LAMP detection was compared between agarose gel electrophoresis (the standard method) and the LFD test. The A31P-LAMP-LFD test was randomly performed on seven cats (four with the A31P mutation and three wild-type cats).

Results

The A31P-LAMP procedure was able to distinguish between cats with MYBPC3-A31P wild-type cats and MYBPC3-A31P mutant cats. The LAMP reactions were able to be completed in 60 min at a single temperature of 64◦C. Moreover, this study demonstrated that A31P-LAMP coupled with the LFD test allowed for A31P genotype detection at a lower DNA concentration than agarose gel electrophoresis.

Discussions

This new A31P-LAMP with a LFD test is a successful and reliable assay with a rapid method, cost-effectiveness, and low requirements for sophisticated equipment for the detection of MYBPC3-A31P mutations. Thus, this assay has excellent potential and can be recognized as a novel screening test for hypertrophic cardiomyopathy associated with MYBPC3-A31P mutations in felines.

Prevalence of cardiac myosin-binding protein C3 mutations in Maine Coon cats with hypertrophic cardiomyopathy

Background and Aim:

Hypertrophic cardiomyopathy (HCM) is a common heart problem that affects many cats. Although cats with HCM are symptomatic, some die suddenly or develop congestive heart failure. Therefore, this study aimed to estimate the prevalence of myosin-binding protein C3 (MYBPC3), A31P, and A74T polymorphisms in Maine Coon cats to assess risk factors for diagnosing HCM in cats.

Materials and Methods:

Forty-nine Maine Coon cats of at least 10 months of age were enrolled in this study. First, clinical parameters, such as heart rate, systolic blood pressure, and echocardiography, were evaluated. Then, polymerase chain reaction, followed by DNA sequencing, was conducted using specific primers for amino acid substitutions caused by genetic variants of MYBPC3-A31P and -A74T polymorphisms.

Results:

Investigations showed that the prevalence of MYBPC3-A31P and -A74T mutations in this study was 16.33% and 24.45%, respectively. Moreover, HCM in cats with MYBPC3-A31P and A74T mutations increased with age, body weight, high heart rate, and prolonged isovolumic relaxation time.

Conclusion:

Therefore, we propose that Maine Coon cats develop HCM due to multiple genetic factors and underlying clinical characteristics in individual cats. Furthermore, relaxation time assessments can be a sensitive technique for HCM screening during its preclinical phase and can help identify the risk of developing HCM. However, further studies are warranted to evaluate the effect of MYBPC3 mutations on the phenotypic expression of HCM.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Genetics of feline hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by an abnormal increase in myocardial mass that affects cardiac structure and function. HCM is the most common inherited cardiovascular disease in humans (0.2%) and the most common cardiovascular disease in cats (14.7%). Feline HCM phenotype is very similar to the phenotype found in humans, but the time frame for the development of the disease is significantly shorter. Similar therapeutic agents are used in its treatment and it has the same complications, such as heart failure, thromboembolism and sudden cardiac death. In contrast to humans, in whom thousands of genetic variants have been identified, genetic studies in cats have been limited to fragment analysis of two sarcomeric genes identifying two variants in MYBPC3 and one in MYH7. Two of these variants have also been associated with human disease. The high prevalence of the reported variants in non-affected cats hinders the assumption of their pathogenicity in heterozygotes. An in-depth review of the literature about genetic studies on feline HCM in comparison with the same disease in humans is presented here. The close similarity in the phenotype and genotype between cats and humans makes the cat an excellent model for the pathophysiological study of the disease and future therapeutic agents.

The use of focused cardiac ultrasound to screen for occult heart disease in asymptomatic cats

Background

Focused cardiac ultrasound (FCU) helps detect occult heart disease in human patients.

Hypothesis

Focused cardiac ultrasound by a nonspecialist practitioner (NSP) will increase the detection of occult heart disease in asymptomatic cats compared with physical examination and ECG.

Animals

Three hundred forty‐three client‐owned cats: 54 excluded and 289 analyzed.

Methods

Multicenter prospective cohort study. Twenty‐two NSPs were trained to perform FCU. Cats without clinical signs of heart disease were recruited, and NSPs performed the following in sequential order: physical examination, ECG, FCU, and point‐of‐care N‐terminal pro‐B‐type natriuretic peptide assay (POC‐BNP). After each step, NSPs indicated yes, no, or equivocal as to whether they believed heart disease was present. The level of agreement between the NSP diagnosis and a blinded cardiologist's diagnosis after echocardiogram was evaluated using Cohen's kappa test.

Results

Cardiologist diagnoses included 148 normal cats, 102 with heart disease, and 39 equivocal ones. Agreement between NSP and cardiologist was slight after physical examination (kappa 0.253 [95% CI, 0.172‐0.340]), did not increase after ECG (0.256 [0.161‐0.345]; P = .96), increased after FCU (0.468 [0.376‐0.558]; P = .002), and the level of agreement was similar after POC‐BNP (0.498 [0.419‐0.580]; P = .67). In cats with mild, moderate, and marked occult heart disease, the proportion of cats having a NSP diagnosis of heart disease after FCU was 45.6%, 93.1%, and 100%, respectively.

Conclusions and Clinical Importance

Focused cardiac ultrasound performed by NSPs increased the detection of occult heart disease, especially in cats with moderate to marked disease. Focused cardiac ultrasound appears to be a feasible and useful tool to assist NSPs in the detection of heart disease in cats.

Speckle tracking echocardiography in cats with preclinical hypertrophic cardiomyopathy

Background

Cats with hypertrophic cardiomyopathy (HCM) have decreased left ventricular (LV) longitudinal deformation detected by mitral annular plane systolic excursion (MAPSE) and speckle tracking echocardiography. People with preclinical HCM have decreased systolic LV longitudinal and radial strain (S) and strain rate (SR), with preserved circumferential S and SR.

Hypothesis/Objectives

Cats with preclinical HCM have decreased systolic LV deformation compared to normal cats.

Animals

Seventy‐three client‐owned cats with (n = 37) and without (n = 36) preclinical HCM.

Methods

Retrospective echocardiographic study. Left and right ventricular longitudinal S and SR, LV radial and circumferential S and SR were calculated by STE. Left ventricular mass was also calculated. Correlation between STE variables and LV hypertrophy was determined and receiver‐operating characteristic (ROC) curves were plotted for prediction of HCM.

Results

Cats with HCM had smaller absolute longitudinal S (−14.8 ± 3.3% vs −19.7 ± 2.7%, P < .001), longitudinal SR (−2.36 ± 0.62 vs −2.95 ± 0.68 second⁻¹, P < .001), radial S (46.2 ± 21.3% vs 66.7 ± 17.6%, P < .001), and radial SR (5.60 ± 2.08 vs 6.67 ± 1.8 second⁻¹, P < .001) compared to healthy controls. No difference was observed for circumferential S and SR. Cats with HCM had greater LV mass (13.2 ± 3.7 g vs 8.6 ± 2.7 g, P < .001). The ROC with the greatest area under the curve (AUC) for the identification of HCM (0.974) was plotted from a logistic regression equation combining LV mass, MAPSE at the free wall, and LV internal diameter in diastole (LVIDd).

Conclusions and clinical importance

Cats with preclinical HCM have decreased long axis and radial deformation. Decreased longitudinal deformation and decreased LVIDd are factors that would support a diagnosis of HCM.

Holter monitoring demonstrates that ventricular arrhythmias are common in cats with decompensated and compensated hypertrophic cardiomyopathy

Arrhythmias can complicate cardiac disease in cats and are a potential cause of sudden death. The aim of this study was to evaluate the presence and nature of cardiac arrhythmias, and the potential correlation between plasma serum troponin I (cTnI) concentrations and the presence or severity of arrhythmias in cats with decompensated (dHCM) and compensated hypertrophic cardiomyopathy (cHCM). Forty one client-owned cats were studied: 16 with cHCM, 15 with dHCM and 10 healthy control cats. Physical examination, echocardiography, cTnI and 24-h Holter recordings were obtained in all cats and thoracic radiographs in cats with dHCM. Cats in both HCM groups were followed for 1 year after their initial Holter examination. The median (range) number of ventricular premature complexes (VPCs) over 24h was 867 (1-35,160) in cats with dHCM, 431 (0-18,919) in cats with cHCM and 2 (0-13) in healthy control cats. The median number of episodes of ventricular tachycardia (VTach) was 0 (0-1497) in dHCM and 0.5 (0-91) in cats with cHCM. The number of VPCs, VTach episodes and heart rate was not different between the HCM groups. Plasma serum troponin I was highest in the cats with dHCM, but there was no correlation between cTnI concentration and the number of arrhythmias. Thirteen of 31 cats with HCM died, but an association with the presence and complexity of ventricular arrhythmias was not observed. Compared to healthy cats, ventricular arrhythmias were common in cats with cHCM and dHCM, but neither presence nor complexity of arrhythmias could be linked to prognosis.

Investigations into the Sarcomeric Protein and Ca2+-Regulation Abnormalities Underlying Hypertrophic Cardiomyopathy in Cats (Felix catus)

Hypertrophic cardiomyopathy (HCM) is the most common single gene inherited cardiomyopathy. In cats (Felix catus) HCM is even more prevalent and affects 16% of the outbred population and up to 26% in pedigree breeds such as Maine Coon and Ragdoll. Homozygous MYBPC3 mutations have been identified in these breeds but the mutations in other cats are unknown. At the clinical and physiological level feline HCM is closely analogous to human HCM but little is known about the primary causative mechanism. Most identified HCM causing mutations are in the genes coding for proteins of the sarcomere. We therefore investigated contractile and regulatory proteins in left ventricular tissue from 25 cats, 18 diagnosed with HCM, including a Ragdoll cat with a homozygous MYBPC3 R820W, and 7 non-HCM cats in comparison with human HCM (from septal myectomy) and donor heart tissue. Myofibrillar protein expression was normal except that we observed 20-44% MyBP-C haploinsufficiency in 5 of the HCM cats. Troponin extracted from 8 HCM and 5 non-HCM cat hearts was incorporated into thin filaments and studied by in vitro motility assay. All HCM cat hearts had a higher (2.06 ± 0.13 fold) Ca²⁺-sensitivity than non-HCM cats and, in all the HCM cats, Ca²⁺-sensitivity was not modulated by troponin I phosphorylation. We were able to restore modulation of Ca²⁺-sensitivity by replacing troponin T with wild-type protein or by adding 100 μM Epigallocatechin 3-gallate (EGCG). These fundamental regulatory characteristics closely mimic those seen in human HCM indicating a common molecular mechanism that is independent of the causative mutation. Thus, the HCM cat is a potentially useful large animal model.

Investigations into the Sarcomeric Protein and Ca2+-Regulation Abnormalities Underlying Hypertrophic Cardiomyopathy in Cats (Felix catus)

Hypertrophic cardiomyopathy (HCM) is the most common single gene inherited cardiomyopathy. In cats (Felix catus) HCM is even more prevalent and affects 16% of the outbred population and up to 26% in pedigree breeds such as Maine Coon and Ragdoll. Homozygous MYBPC3 mutations have been identified in these breeds but the mutations in other cats are unknown. At the clinical and physiological level feline HCM is closely analogous to human HCM but little is known about the primary causative mechanism. Most identified HCM causing mutations are in the genes coding for proteins of the sarcomere. We therefore investigated contractile and regulatory proteins in left ventricular tissue from 25 cats, 18 diagnosed with HCM, including a Ragdoll cat with a homozygous MYBPC3 R820W, and 7 non-HCM cats in comparison with human HCM (from septal myectomy) and donor heart tissue. Myofibrillar protein expression was normal except that we observed 20–44% MyBP-C haploinsufficiency in 5 of the HCM cats. Troponin extracted from 8 HCM and 5 non-HCM cat hearts was incorporated into thin filaments and studied by in vitro motility assay. All HCM cat hearts had a higher (2.06 ± 0.13 fold) Ca²⁺-sensitivity than non-HCM cats and, in all the HCM cats, Ca²⁺-sensitivity was not modulated by troponin I phosphorylation. We were able to restore modulation of Ca²⁺-sensitivity by replacing troponin T with wild-type protein or by adding 100 μM Epigallocatechin 3-gallate (EGCG). These fundamental regulatory characteristics closely mimic those seen in human HCM indicating a common molecular mechanism that is independent of the causative mutation. Thus, the HCM cat is a potentially useful large animal model.