The Impact of Two TNXB Variants on the Development of Arterial Aneurysms, Dissection, and Bicuspid Aortic Valve

Introduction: Genetic variants in the Tenascin-XB (TNXB) gene have been associated with autosomal recessive Ehlers-Danlos Syndrome (classical-like) without vascular features. Here, we report the contribution of two TNXB variants, in cis or trans, to the development of arterial aneurysms and bicuspid aortic valves with or without connective tissue disease features present. Methods: The identification of compound heterozygosity in TNXB (c.8791+1G>A, c.12469+2T>C) in a 52-year-old female with fibromuscular dysplasia, bilateral vertebral artery dissections, and thoracic aortic aneurysm by whole exome sequencing (WES) prompted screening for TNXB variants in an institutional WES registry comprising 350 individuals with aneurysms and/or dissections. Multigene panel testing (MGPT) results from 1844 individuals tested at Ambry Genetics for a personal or family history of aneurysms, dissections, or other connective tissue disease features were used for replication analysis. Random exomes of 26,922 unaffected individuals were used as controls. Statistical analysis using Fisher’s exact test was carried out to compare the frequency of two or more TNXB variants in cases vs. controls. AlphaFold3 structural modeling was used to assess the effects of variants in cis on the 3-D structure and molecular interaction with the TGF-beta-3 proprotein. Results: There were significantly higher numbers of individuals who carried two or more rare, nonsynonymous TNXB variants, in cis or trans, in both WES (n=5/350; 1.4%) and MGPT (n=19/1844, 1.0%) datasets (p<0.01) compared to ethnically matched controls (n=89/26922; 0.14%). Additionally, there was a significantly higher prevalence of bicuspid aortic valve (BAV) in the MGPT cohort compared to the general population (11% vs. <2 % reported). The analysis by AlphaFold3 structural modeling revealed increased distortion of the 3-D structure caused by the presence of two variant(s) in cis vs. one variant in TNXB. Conclusion: This data strongly suggests an association between vascular aneurysm and/or dissection or bicuspid aortic valves and individuals with two TNXB variants.