TGFB1 and Marfan syndrome: In this study, we systematically dissect the effects of ERK signalling downstream of TGF‐β to: (a) compare ERK signalling in aneurysmal aortic root vs non‐dilated ascending aortic specimens from human MFS patients; (b) analyse the relative contributions of Smad and ERK to known SMC phenotype changes in MFS; and (c) identify downstream ERK‐dependent pathways in primary cultured MFS SMCs to further elucidate the role of TGF‐β signalling during aneurysm formation.