Bicuspid Aortic Valve: Old and Novel Gene Contribution to Disease Onset and Complications

Background: Bicuspid aortic valve (BAV) is the most common congenital heart defect, and its complications (namely, dilatation of the thoracic ascending aorta) raise concerns regarding the proper timing of aortic surgery. The study aim is to unravel the genetic basis of BAV and its complications through a high-throughput sequencing (HTS) approach and segregation analysis if family members were available. Methods: Fifty-two Italian BAV patients were analyzed by HTS using the Illumina MiSeq platform. Targeted sequencing of 97 genes known to be or plausibly associated with connective tissue disorders or aorthopathy was performed. Thirty-five first-degree relatives of N = 10 probands underwent mutational screening for variants identified in the index cases. Results: HTS identified 194 rare (MAF < 0.01) variants in 63 genes. Regarding previously reported genes, five NOTCH1 variants in four BAV patients, four FBN1 variants in two patients and one GATA5 variant in one patient were identified. Interestingly, among further loci, the possible contribution of PDIA2, LRP1 and CAPN2 was suggested by (a) the increased prevalence of rare genetic variants, independently from their ACMG classification in the whole BAV cohort, and (b) segregation analyses of variants identified in family members. Moreover, the present data also suggest the possible contribution of rare variants to BAV complications, specifically MYLK in aortic dilatation, CAPN2 in BAV calcification and VHL and AGGF1 in valve stenosis. Conclusions: Our results underline clinical and genetic diagnosis complexity in traits considered monogenic, such as BAV, but characterized by variability in disease phenotypic expression (incomplete penetrance), as well as the contribution of different major and modifier genes to the development of complications.