Genetic Cardiomyopathies¶
Chapter 267 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- Genetic cardiomyopathies account for 30-50% of all cardiomyopathy cases, with autosomal dominant inheritance being most common.
- Key genetic defects include sarcomere proteins (ACTC1, MYH7, MYBPC3), desmosomal proteins (DSP, DSG2), and nuclear membrane proteins (LMNA).
- Diagnosis requires comprehensive evaluation including family history, imaging (echo, MRI), and genetic testing with multigene panels.
- Treatment is phenotype-driven, with beta-blockers, calcium channel blockers, and septal reduction therapies (myectomy/ablation) for obstructive cases.
- Prognosis varies by subtype, with sudden cardiac death risk up to 1% annually in high-risk patients.
1. DEFINITION & OVERVIEW¶
Genetic cardiomyopathies are inherited disorders of cardiac muscle structure/function caused by mutations in genes encoding sarcomeric proteins, desmosomal proteins, or nuclear membrane components. These conditions include hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and restrictive cardiomyopathy (RCM).
Table 266-2: Initial Evaluation of Cardiomyopathy¶
| Clinical Evaluation | Laboratory Evaluation | Imaging | Special Tests |
|---|---|---|---|
| Thorough history/physical | Electrocardiogram | 2D/ Doppler echo | Genetic counseling/testing |
| Family history of heart failure/sudden death | Serum electrolytes, BUN/creatinine | MRI for fibrosis | Multigene panel |
| Alcohol/drug use history | Lipid profile, TSH | Endomyocardial biopsy | Respiratory pathogen panel |
| Activity tolerance assessment | Iron studies, urinalysis | Coronary angiography | Serologies for infections |
1.1 Genetic Basis¶
Over 100 genes are implicated in cardiomyopathies. Autosomal dominant (AD) inheritance is most common (e.g., MYH7, MYBPC3), with ~80% of patients having variants in these genes. X-linked (e.g., DMD, GLA) and autosomal recessive (e.g., TAZ, FXN) patterns also occur.
1.2 Clinical Spectrum¶
Phenotypes range from isolated cardiomyopathy to multisystem disorders (e.g., Danon disease with skeletal myopathy). Age-dependent penetrance and variable expressivity are common, with males often showing more severe disease.
2. EPIDEMIOLOGY¶
Prevalence of genetic cardiomyopathies is ~1:500 in North America/Africa/Asia. HCM is the most common, with 10-20% of cases having familial inheritance. DCM has a prevalence of ~1:2500, with 25-30% of cases having genetic etiology.
Table 267-2: Risk Stratification for Sudden Death in HCM¶
| Major Risk Factor | Screening Technique |
|---|---|
| History of cardiac arrest | Echocardiography |
| Family history of sudden death | Genetic testing |
| LV thickness >30 mm | Echocardiography |
| LV systolic dysfunction (EF <50%) | Echocardiography |
| LV outflow tract gradient >30 mmHg | Echocardiography |
2.1 Risk Factors¶
Family history of cardiomyopathy, sudden cardiac death, or arrhythmias. Male sex increases penetrance for most variants. Certain ethnic groups show founder mutations (e.g., MYBPC3 in Ashkenazi Jews).
2.2 Demographics¶
HCM typically presents in 20-40 years, with 30% of carriers developing hypertrophy after 70 years. DCM often presents in 30-60 years, with 25% of familial cases having truncating TTN variants.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Genetic defects disrupt sarcomere structure/function, desmosomal integrity, or nuclear membrane stability. Mutations in sarcomere proteins (e.g., MYH7) cause enhanced calcium sensitivity and impaired relaxation. Desmosomal defects (e.g., DSP) lead to myocyte disarray and fibrosis. Nuclear membrane defects (e.g., LMNA) cause cardiomyopathy with skeletal myopathy.
Table 267-1: Selected Genetic Defects Associated with Cardiomyopathy¶
| Gene Product | Inheritance | Cardiac Phenotype | Extracardiac Manifestations |
|---|---|---|---|
| ACTC1 (cardiac actin) | AD | HCM, DCM | Yes |
| MYH7 (b myosin heavy chain) | AD | HCM, DCM, LVNC | Skeletal myopathy |
| MYBPC3 (myosin binding protein C) | AD | HCM | Yes |
| TNNT2 (cardiac troponin T) | AD | HCM, DCM, LVNC | Yes |
| TNNI3 (cardiac troponin I) | AD, AR | HCM, DCM, RCM | Yes |
3.1 Sarcomere Mutations¶
ACTC1, MYH7, MYBPC3, TNNI3, TTN, and TPM1 variants cause HCM and DCM. These mutations alter calcium handling, increase energy demand, and disrupt myocyte alignment.
4. CLINICAL FEATURES¶
Symptoms include dyspnea, chest pain, syncope, and heart failure. Physical exam findings may show S3 gallop, systolic murmur, or signs of heart failure. ECG abnormalities include left ventricular hypertrophy, arrhythmias, and conduction delays.
4.1 Hypertrophic Cardiomyopathy¶
Asymmetric septal hypertrophy, left ventricular outflow tract obstruction, and diastolic dysfunction. 30% of patients have obstructive physiology with systolic anterior motion of the mitral valve.
4.2 Dilated Cardiomyopathy¶
Global left ventricular dilation, reduced ejection fraction (<50%), and systolic dysfunction. May present with heart failure, arrhythmias, or sudden death.
5. DIFFERENTIAL DIAGNOSIS¶
Differentiate from non-genetic cardiomyopathies (e.g., alcoholic, ischemic), infiltrative diseases (e.g., sarcoidosis), and metabolic disorders (e.g., Fabry disease). Consider congenital heart disease and valvular disorders.
5.1 Cardiomyopathy Mimics¶
Athlete's heart (physiologic hypertrophy), hypertensive heart disease, and amyloidosis. Genetic testing helps distinguish these from inherited forms.
5.2 Arrhythmogenic Disorders¶
Distinguish ARVC from DCM using ECG findings (epsilon waves, T-wave inversions) and imaging (right ventricular dilation).
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic workup includes echocardiography, cardiac MRI, ECG, and genetic testing. Cardiac MRI detects fibrosis and late gadolinium enhancement. Genetic testing identifies pathogenic variants in ~80% of familial cases.
Variables Utilized in the European Society of Cardiology Risk Calculator¶
| Parameter | Measurement |
|---|---|
| LV outflow tract gradient | Peak gradient (mmHg) |
| Left atrial diameter | Parasternal long axis (mm) |
| LV wall thickness | Maximal wall thickness (mm) |
| Age | Years |
| Syncope | History |
| Nonsustained VT | Ambulatory ECG recording |
6.1 Imaging¶
Echocardiography for LV dimensions, systolic function, and outflow tract gradients. Cardiac MRI for fibrosis, myocardial inflammation, and late gadolinium enhancement.
6.2 Genetic Testing¶
Multigene panels (e.g., CardioMyoGen) detect ~80% of pathogenic variants. Confirmatory testing includes Sanger sequencing and variant classification (pathogenic, likely pathogenic).
7. MANAGEMENT & TREATMENT¶
Symptomatic management includes beta-blockers, calcium channel blockers, and antiarrhythmics. Septal reduction therapies (myectomy/ablation) for obstructive HCM. Implantable cardioverter-defibrillators (ICDs) for high-risk patients.
Treatment Algorithm for Hypertrophic Cardiomyopathy¶
| Step | Action |
|---|---|
| 1 | Evaluate sudden death risk (ICD consideration) |
| 2 | Treat obstructive physiology with beta-blockers/verapamil |
| 3 | Consider septal ablation/myectomy for refractory symptoms |
| 4 | Manage heart failure with diuretics and afterload reduction |
| 5 | Monitor for arrhythmias and anticoagulate for AF |
7.1 Pharmacologic Therapy¶
Beta-blockers (metoprolol, propranolol) reduce heart rate and contractility. Verapamil for diastolic dysfunction. Disopyramide for refractory symptoms. Mavacamten for obstructive HCM.
7.2 Surgical Options¶
Septal myectomy for severe outflow tract obstruction. Alcohol septal ablation for selected patients. ICD implantation for sudden death prevention in high-risk patients.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by subtype. HCM has 1% annual sudden death risk, while DCM has higher mortality. Complications include heart failure, arrhythmias, and thromboembolism. Genetic testing improves risk stratification.
8.1 Survival Rates¶
5-year survival for HCM is ~95% with optimal management. DCM has 50-70% survival with heart failure therapy. ARVC has 50% 10-year survival without ICD.
8.2 Long-term Outcomes¶
Progressive fibrosis and ventricular dilation in DCM. Risk of sudden death increases with age and severity of left ventricular dysfunction.
9. SPECIAL CONSIDERATIONS¶
Pregnancy management requires close monitoring for heart failure and arrhythmias. Pediatric cases may present with atypical features. Elderly patients face higher risks of complications from invasive therapies.
9.1 Pregnancy¶
Beta-blockers are preferred for maternal management. ICDs may require adjustment during pregnancy. Risk of sudden death remains elevated.
9.2 Pediatric Presentation¶
Early-onset cases may show restrictive physiology or arrhythmias. Genetic testing is critical for family screening.
10. KEY POINTS & CLINICAL PEARLS¶
- Genetic testing is essential for family screening and risk stratification.
- Management is phenotype-driven with ICDs for high-risk patients.
- Cardiac MRI is critical for diagnosing fibrosis and differentiating subtypes.
- Mavacamten represents a breakthrough in obstructive HCM therapy.
- Multigene panels detect ~80% of pathogenic variants in familial cases.