Genetic Testing After Heart Transplantation Uncovers Heritable Disease and Drives Family Screening

BACKGROUND: Genetic testing (GT) is established in ambulatory cardiomyopathy (CM), but its utility after heart transplantation (HTx) recipients remains poorly characterized. OBJECTIVES: This study aimed to evaluate the clinical utility of GT in adult HTx recipients with CM, focusing on etiologic reclassification, family cascade screening, and the genetic architecture of end-stage disease. METHODS: GenbaseHTx is a nationwide, multicenter retrospective study of adult HTx recipients transplanted for CM across 12 Spanish centers (2010-2023). GT results were centrally adjudicated using American College of Medical Genetics and Genomics criteria. Outcomes included prevalence of pathogenic/likely pathogenic variants, etiologic reclassification after GT, and cascade screening activation. RESULTS: Among 657 HTx recipients, a pathogenic/likely pathogenic variant was identified in 53% (351/657). GT led to etiologic reclassification in 35% (231/657) (42% when performed post-HTx -106/253-). Family screening (performed in 69% of families -224/328-) identified affected relatives in 22% (19/90) of genotype-negative and 42% (49/107) of genotype-positive cases. Notably, a genetic etiology was identified in 36% (15/42) of CM initially attributed to acquired or "second-hit" causes. In dilated cardiomyopathy, the genetic architecture of transplanted patients differed from ambulatory cohorts, with lower TTN variant prevalence and enrichment of arrhythmogenic genes. CONCLUSIONS: GT remains clinically actionable after HTx, enabling etiologic reclassification and driving cascade screening. These findings support systematic GT in HTx recipients with CM, including those with prior environmental triggers or second-hit etiologies, and regardless of time from transplantation.