Pathogenicity assessment of a bicuspid aortic valve-associated

Introduction: Bicuspid aortic valve (BAV) is one of the most common congenital heart defects but its genetic basis remains incompletely defined. Extracellular matrix components play key roles in outflow tract (OFT) and valve development, but their contribution to BAV is not fully established. Following the analysis of a cohort of BAV patients, we identified a family harbouring a rare human ELASTIN (ELN) variant (p.Gln691X). Here, we investigated the pathogenicity of this variant using an in vivo zebrafish model. Methods: We generated a zebrafish elna/b double knockout (KO) using an RNAless CRISPR Cas9 strategy to avoid genetic compensation. Cardiovascular morphology and function were assessed in mutant embryos. To evaluate pathogenicity of the human ELN p.Gln691X variant, mutant and control embryos were rescued by mRNA injection encoding either WT human ELN or the p.Gln691X variant. Results: elna/b double KO zebrafish exhibited cardiovascular defects including OFT anomalies, reduced stroke volume and dysmorphic aortic valves, highlighting Elastin's critical role in cardiac development. We then used this model to test the ELN variant identified in the BAV family. We found that wild-type ELN mRNA was able to restore normal cardiac function and morphology, whereas the variant ELN mRNA failed to do so. Discussion: Our study establishes a robust in vivo model to assess ELN variant pathogenicity and provides evidence linking ELASTIN to BAV, opening new avenues for uncovering the genetic mechanisms underlying BAV.