NEB mutation and arrhythmic risk in mitral valve prolapse: phenotypic insights using speckle tracking echocardiography

Background Arrhythmic mitral valve prolapse (AMVP) has been linked to abnormal valvular-myocardial mechanics with localized traction by the prolapsing leaflets, particularly in the presence of mitral annular disjunction (MAD). However, initial familial studies of AMVP point to a diffuse myopathic process that is independent of mitral regurgitation (MR) severity. Purpose To assess the association of AMVP genes with imaging-derived markers of early myocardial dysfunction in a large cohort of familial and sporadic MVP cases. Methods We analyzed 310 individuals (32 AMVP probands and 158 family members) across 37 duos/trios/extended pedigrees, as well as 130 sporadics. Participants underwent whole exome sequencing, 48-hour Holters, and two-dimensional/speckle-tracking echocardiography. We assessed valve characteristics, MAD, global longitudinal strain, and mechanical dispersion (MD), a measure of heterogenous contraction/electrical dispersion. Variant filtering prioritized rare (MAF <0.1%) disruptive coding variants in genes with high loss-of-function intolerance (pLI >0.9). Variants were retained if they met ACMG/AMP co-segregation criteria. We first conducted within-family analyses to identify genes with rare disruptive variants present in ≥ 3 AMVPs and absent in non-AMVPs. Genes functionally linked to the strongest candidate were identified using the STRING protein association network. Finally, the broader cohort was stratified by presence of rare disruptive variants within this gene network. Results A rare disruptive variant in the NEB gene (rs556624010), which encodes nebulin – a sarcomeric protein – emerged as the strongest candidate in the most arrhythmic MVP pedigree (R pedigree – Figure 1). Specifically, the rs556624010 variant was present in all AMVPs, including 2 with sudden cardiac arrest, and was absent in non-AMVP relatives. Rare disruptive variant in the same gene was also identified in another pedigree with a history of PVC ablation in the proband and polymorphic PVCs in 2 family members. STRING network analysis identified multiple genes functionally associated with NEB (DMD, TMOD4, TTN). Sixteen individuals were found to carry rare disruptive variants within this expanded network of NEB + associated genes. Among these carriers, the prevalence of either frequent/complex ventricular ectopy was 63% compared to 36% in the non-carriers (p<0.001) (Table 1). Increased MD (defined as >70ms, 2SD above normal), was observed in 38% vs. 14% (p=0.02). None of the carriers had severe MR and MAD was present in the minority of cases (Table 1). Conclusion In MVP, rare variants of NEB and its functional gene network are associated with greater arrhythmic risk and increased mechanical dispersion even in the absence of significant MR or MAD. These findings suggest a genetically mediated myocardial substrate in AMVP and highlight mechanical dispersion as a sensitive imaging marker to detect subclinical myocardial involvement in this context.