Cardiomyopathy-related genetic variants in wild-type transthyretin cardiac amyloidosis

Background Wild-type transthyretin cardiac amyloidosis (ATTRwt) manifests as restrictive cardiomyopathy and is defined by the absence of TTR mutations. The potential influence of variants in other cardiomyopathy-associated genes remains unexplored, potentially explaining the clinical heterogeneity observed among ATTRwt patients. Purpose To investigate the prevalence of cardiomyopathy-related genetic variants in patients with ATTRwt cardiomyopathy (CM) presenting complex or atypical phenotypes and to assess their potential influence on clinical phenotype. Methods We analyzed 331 ATTR-CM patients (median age 79.0 years [IQR: 75.0-83.0]; 83.7% male) for TTR gene, identifying 11 (3.3%) ATTRv (median age 75.0 years [IQR: 60.5-78.5]) and 320 (96.7%) ATTRwt cases (median age 80.0 years [IQR: 75.0-83.0]). A subset of 25 ATTRwt patients underwent additional next-generation sequencing (NGS). Variants were classified using ACMG criteria with a specialized framework for VUS interpretation as likely pathogenic/pathogenic (LP/P), variant of unknown significance highly suspicious of pathogenicity (VUS/LP), or VUS. Statistical analyses were performed using R version 4.1.0. Results NGS revealed variants in CM-related genes in 6/25 (diagnostic yield: 24%) ATTRwt patients: 2 had LP/P in MYBPC3 and TTN, 3 carried VUS/LP in TPM1, MYH7, and DSC2, and one patient had two VUS in RYR2 and ANK2. ATTRwt presented significantly older compered to ATTRv (78.2 vs. 68.3 years, p=0.012); however, within ATTRwt NGS tested, patients with genetic variants presented at a significantly younger age compared to those without (60.3±7.5 vs. 71.9±7.4 years; p<0.015) (Figure1). Gene enrichment analysis showed that the identified genes are predominantly expressed in heart tissue and linked primarily to dilated and hypertrophic cardiomyopathy. Key molecular functions include actin binding and calcium ion binding, essential for contractile function (Figure2). Conclusion A substantial proportion of ATTRwt harbour CM-related genetic variants that appear to influence disease onset, with affected patients presenting approximately 11.6 years earlier than those without CM-variants. This finding suggests these variants could be act as genetic modifiers of ATTRwt presentation. Our findings support the value of phenotype-driven extended genetic analysis beyond TTR sequencing in selected ATTRwt patients, particularly those with complex phenotypes, atypical presentations, or earlier disease onset. These insights into the genetic landscape of ATTR amyloidosis reveal previously unrecognized contributors to disease heterogeneity and may guide more personalized approaches to risk stratification and management.