Tenascin-X (TNX), which has a molecular mass of roughly 450 kDa, is the largest member of the tenascin family. Complete deficiency of TNX in humans leads to a recessive form of Ehlers-Danlos syndrome (EDS). TNX is expressed abundantly in a variety of tissues, especially in cardiac muscle and in perivascular stroma. Human TNX is also present in serum with an apparent molecular size of 140 kDa. In the present study, we investigated the expression levels of TNX protein in thoracic and abdominal

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... tic aneurysm tissues. The level of TNX was significantly increased in both aortic aneurysm tissues compared with that in adjacent normal tissues. Next, to compare TNX levels in serum from both patients with thoracic aortic aneurysm and patients with abdominal aortic aneurysm with levels in serum from healthy individuals, we developed a sandwich enzyme-linked immunosorbent assay (ELISA) using TNX-specific antibodies. Measurement of TNX serum concentrations in both aortic aneurysm patients and controls showed that the levels were almost the same. These results indicate that TNX expression is significantly elevated in both thoracic and abdominal aortic aneurysm tissues but that the increase in TNX levels in both tissues does not result in an increase in TNX serum concentration in patients with TAA or AAA.