The Loeys-Dietz syndrome (LDS) is an inherited connective tissue disorder caused by mutations in the transforming growth factor (TGF-) receptors TGFBR1 or TGFBR2. Most patients with LDS develop severe aortic aneurysms resulting in early need of surgical intervention. We investigated circulating outgrowth endothelial cells (OEC) from the peripheral blood of LDS to gain further insight into the pathophysiology of the disorder. We performed gene expression profiling using microarray analysis followed by quantitative PCR for verification of gene expression. OECs isolated from age- and sex-matched healthy donors served as reference control.