A rare, genetic, aortic malformation defined as a presence of abnormal two-leaflet aortic valve in at least 2 first-degree relatives. It is frequently asymptomatic or may be associated with progressive aortic valve disease (aortic regurgitation and/or aortic stenosis, typically due to valve calcification) and a concomitant aortopathy (i.e. aortic dilation, aortic aneurysm and/or dissection).