Maegdefessel et al. showed that modulating microRNA-21 expression reduces cell proliferation, protecting mice from AAA expansion.16 Smooth muscle cell de-differentiation and proliferation is an early event in AAA.17 Preventing this event by deleting Kruppel-like factor-4 prevents AAA formation in mice.18 These data point to a period of pathological cellular remodeling in early AAA and suggest that anti-proliferative therapy might be beneficial. Here, KLF4 is linked to triple-A syndrome.