However, this study identified Tie-2, the receptor of Ang-1 and Ang-2, as a crucial factor in the development or maintenance of coronary collateral vessels in severe CAD as more production of Tie-2 within the coronary circulation was related to well developed coronary collateral.[30] As a result, further study on the Ang/Tie-2 system is necessary for exploration of new therapeutic target for coronary angiogenesis. This evidence concerns the gene ANGPT1 and coronary artery disorder.