%0 Journal Article %T ROBO4 variants predispose individuals to bicuspid aortic valve and thoracic aortic aneurysm %J - %D 2018 %R https://doi.org/10.1038/s41588-018-0265-y %X Bicuspid aortic valve (BAV) is a common congenital heart defect (population incidence, 1¨C2%)1,2,3 that frequently presents with ascending aortic aneurysm (AscAA)4. BAV/AscAA shows autosomal dominant inheritance with incomplete penetrance and male predominance. Causative gene mutations (for example, NOTCH1, SMAD6) are known for ¡Ü1% of nonsyndromic BAV cases with and without AscAA5¨C8, impeding mechanistic insight and development of therapeutic strategies. Here, we report the identification of variants in ROBO4 (which encodes a factor known to contribute to endothelial performance) that segregate with disease in two families. Targeted sequencing of ROBO4 showed enrichment for rare variants in BAV/AscAA probands compared with 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. This is consistent with BAV/AscAA-associated findings in patients and in animal models deficient for ROBO4. These data identify a novel endothelial etiology for this common human disease phenotype %U https://www.nature.com/articles/s41588-018-0265-y