SMAD2 and triple-A syndrome: Different concentrations of IL5 (10–200 ng mL−1) did not affect p‐Smad2/3 activation, as determined by immunoblot analyses (Figure S10A/B, Supporting Information).Therefore, reduced collagen deposition in AAA lesions from Rorafl/flIl7rCre/+ mice (Figure 2G) may associate with increased loss of SMCs from these mice (Figure 2E) due to increased SMC apoptosis (Figure 2I) and reduced SMC proliferation (Figure 2H) rather than interference with p‐Smad2/3 signaling.