ROBO4 Variants Predispose Individuals to Bicuspid Aortic Valve and Thoracic Aortic Aneurysm

Bicuspid aortic valve (BAV) is a common congenital heart defect (population incidence, 1–2%)(1–3) that frequently presents with ascending aortic aneurysm (AscAA)(4). BAV/AscAA shows autosomal dominant inheritance with incomplete penetrance and male predominance. Causative gene mutations are known for ≤1% of nonsyndromic BAV cases with/without AscAA (e.g. NOTCH1, SMAD6)(5–8), impeding mechanistic insight and development of therapeutic strategies. We report the identification of mutations in ROBO4, encoding a factor known to contribute to endothelial performance, that segregate with disease in two families. Targeted sequencing of ROBO4 revealed enrichment for rare variants in BAV/AscAA probands compared to controls. Targeted silencing of ROBO4 or mutant ROBO4 expression in endothelial cell lines results in impaired barrier function and a synthetic repertoire suggestive of endothelial-to-mesenchymal transition (EnMT); concordant BAV/AscAA-associated findings are observed in patients and animal models deficient for ROBO4. These data identify a novel endothelial etiology for this common human disease phenotype.