The discrepancy between AAA and thoracic aortic aneurysm may relate to smooth muscle cells in the thoracic aorta originating from the neural crest and the somitic mesoderm, while smooth muscle cells in the abdominal aorta originate from the splanchnic mesoderm.39 This distinction could in turn lead to divergent responses to injury across the two sites, and thus a differing role for IL6 signaling in driving pathology. The gene discussed is IL6; the disease is thoracic aortic aneurysm.