FBN1 and Marfan syndrome: The finding that KLF2/4 function prevents MVD by restraining TGF-β signaling is remarkable in light of human and mouse MVD conferred by mutations in FBN1 associated with Marfan syndrome, as well as increased TGF-β/Smad signaling observed in human and canine myxomatous valves that arise in the absence of known Marfan syndrome mutations (7, 12, 13, 37, 50–54).