MMP9 and triple-A syndrome: A study found that miR‐181a, miR‐21, miR‐15a‐3p, miR‐30a‐5p and miR‐489‐3p are up‐regulated in aortic wall tissue of AAA patients compared with controls, while miR‐133b, miR‐133a, miR‐331‐3p, miR‐30c‐2 and miR‐204 are significantly down‐regulated.188, 189 Of note, down‐regulation of miR‐133a and miR‐133b is involved with a shift of VSMCs to a proliferative phenotype,190 and the decreased miR‐204 level can improve MMP‐9 in human AAA tissue, and thereby enhance the degradation of the extracellular matrix in AAA.