The lack of phenotype in SMC-specific Bcar1SMKO mice indicates that the aortic aneurysm in Bcar1SM22KO mice may not be due to SMC-specific loss, a conclusion supported by our observation that loss of Bcar1 did not prevent migration or subsequent differentiation of SMC progenitors essential for formation of the pharyngeal arch arteries. Here, BCAR1 is linked to aortic aneurysm.