We report a novel protective function for LH1 against dissecting AAA; LH1 absence results in thrombospondin-1 (encoded by Thbs1) expression upregulation, promotion of the proinflammatory process, increased matrix metalloproteinase (MMP) activity, and severe VSMC apoptosis in the abdominal aorta, ultimately leading to dissecting AAA formation. This evidence concerns the gene THBS1 and triple-A syndrome.