Dilated Cardiomyopathy

About this condition

Dilated cardiomyopathy (DCM) is characterized by left ventricular dilation and systolic dysfunction in the absence of abnormal loading conditions or coronary artery disease. It is the most common indication for heart transplantation worldwide. Prevalence is approximately 1 in 250 to 500. Familial DCM accounts for 20–50% of cases, predominantly with autosomal dominant inheritance. Age-related penetrance is typical — some gene variants show >90% penetrance by the seventh decade. Clinical presentation includes heart failure symptoms, conduction disease, arrhythmias, and risk of sudden cardiac death. LMNA-related DCM is notable for prominent conduction system disease (atrioventricular block, bundle branch blocks) that often precedes overt cardiomyopathy by years.

TTN (titin) encodes the largest known human protein, which spans half the sarcomere and functions as a molecular spring providing elasticity; truncating variants (TTNtv) are the most common genetic cause of DCM, found in 15–25% of cases. LMNA encodes lamin A/C, nuclear envelope proteins critical for gene regulation and nuclear structural integrity; variants cause DCM combined with conduction disease and high arrhythmic risk (4–8% of DCM). SCN5A encodes the cardiac sodium channel; loss-of-function or specific missense variants can cause DCM, sometimes overlapping with Brugada syndrome or conduction disease phenotypes. Over 12 genes have definitive or strong evidence for DCM causation.

Identifying a DCM-causing variant has major clinical and family implications. For TTN truncating variants, the finding confirms a genetic basis and informs counseling; however, interpretation remains challenging because approximately 3% of the general population carries truncating TTN variants. For LMNA variants, earlier and more aggressive heart failure management is warranted, and close monitoring for conduction disease is essential. For SCN5A variants, assessment for Brugada features is important. Cascade testing of relatives identifies asymptomatic mutation carriers who may benefit from early imaging, activity modification, and preventive medical therapy. For families, genetic testing clarifies previously ambiguous clinical pictures and guides prognostication.

TTN truncating variants, LMNA variants, and SCN5A variants operate through distinct mechanisms and carry different prognostic implications — TTN truncations typically later-onset, LMNA typically earlier with conduction disease, SCN5A variable.

Gene locus: TTN (2q31.2), LMNA (1q22), SCN5A (3p22.2)

Standard DCM panels test 30–50 genes but identify mutations in only 20–40% of familial cases. TTN interpretation remains particularly challenging.

TTN is too large and complex for standard sequencing

TTN is the largest human gene with 364 exons spanning 364 kilobases of DNA. Standard panel sequencing often has poor coverage of TTN's repetitive regions, leading to missed variants and false-negative results. Additionally, approximately 3% of the general population carries truncating TTN variants, complicating pathogenicity assessment. TTN missense variants are generally not considered disease-causing, yet they are frequently reported on DCM panels and labeled as variants of uncertain significance. Whole genome sequencing with sufficient depth can capture the complete TTN sequence and enable more accurate variant detection and interpretation.

A finding enables family screening and gene-informed management

When a pathogenic DCM variant is confirmed, it triggers cascade testing of relatives — identifying asymptomatic mutation carriers who may have no cardiac symptoms yet. Gene-specific management applies: LMNA carriers warrant more aggressive monitoring for conduction disease and arrhythmia risk, justifying lower thresholds for ICD implantation. TTN truncating variant carriers may have more variable expressivity but still benefit from activity monitoring and imaging surveillance. SCN5A-related DCM warrants assessment for Brugada features. Early identification of at-risk relatives enables preventive intervention — aggressive heart failure management, arrhythmia surveillance, and ICD placement if warranted — potentially avoiding progression to transplant candidacy.

Heart failure runs in your family, and you're wondering whether it's genetic. That question has a definitive answer — and it changes what your physician monitors and when.