AbstractAimsLMNA‐related dilated cardiomyopathy (DCM) is a rare disease with an incompletely defined phenotype. The phase 3 REALM‐DCM trial evaluated a potential disease‐modifying therapy for LMNA‐related DCM but was terminated due to futility without safety concern. This study utilized pooled data from REALM‐DCM to descriptively characterize the phenotype and progression of LMNA‐related DCM in a contemporary cohort of patients using common heart failure (HF) measures.MethodsREALM‐DCM enrolled patients with stable LMNA‐related DCM, an implanted cardioverter defibrillator or cardiac resynchronization therapy defibrillator, and New York Heart Association (NYHA) Class II/III HF symptoms.ResultsBetween 2018 and 2022, 77 patients took part in REALM‐DCM. The median patient age was 53 years (range: 23–72), and 57% were male. Overall, 88% of patients had a pathogenic or likely pathogenic LMNA variant, and 12% had a variant of uncertain significance with a concordant phenotype. Among patients with confirmed sequencing, 55% had a missense variant. Atrial fibrillation was present in 60% of patients; 79% of all patients had NYHA Class II and 21% had NYHA Class III HF symptoms at baseline. Median (range) left ventricular ejection fraction (LVEF), 6 min walk test (6MWT) distance, Kansas City Cardiomyopathy Questionnaire Overall Summary (KCCQ‐OS) score and N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) concentration at baseline were 42% (23–62), 403 m (173–481), 67 (18–97) and 866 pg/mL (57–5248), respectively. LVEF, 6MWT distance and KCCQ‐OS score were numerically lower in patients who had NYHA Class III versus II symptoms at baseline (LVEF: 38% vs. 43%; 6MWT distance: 326 vs. 413 m; and KCCQ‐OS score: 43 vs. 70), whereas NT‐proBNP concentration was higher (1216 vs. 799 pg/mL). Median follow‐up was 73 weeks (range: 0.4–218; 73 in NYHA Class II and 75 in NYHA Class III). Patients displayed variable change from baseline in 6MWT, KCCQ‐OS and NT‐proBNP values during follow‐up. Overall, 25% of patients experienced ventricular tachycardia, and 8% had ventricular fibrillation. Ten (13%) patients met the composite endpoint of worsening HF (adjudicated HF‐related hospitalization or urgent care visit) or all‐cause death; six had NYHA Class II and four had NYHA Class III at baseline. All‐cause mortality occurred in 6 (8%) patients; three had NYHA Class II and three had NYHA Class III symptoms at baseline.ConclusionsFindings confirm the significant morbidity and mortality associated with LMNA‐related DCM despite the standard of care management. Typical measures of HF, including 6MWT distance, KCCQ‐OS score and NT‐proBNP concentration, were variable but correlated with NYHA class. An unmet treatment need remains among patients with LMNA‐related DCM. NCT03439514.