FBN1 and Marfan syndrome: Two particular mouse models have found considerable utility in studying the aortic phenotype in Marfan syndrome: the hypomorphic Fbn1mgR/mgR mouse (expressing ~15% of the normal fibrillin-1) (2), which presents a severe Marfan-like phenotype including dilatation and rupture early in maturity, and the Fbn1C1041G/+ knock-in mouse (mimicking a specific human mutation) (11), which experiences a less-severe, slowly developing phenotype over the first year of life.