TDRD9 and chronic obstructive pulmonary disease: Using our own (15) and other studies (14, 26) as a resource, we identified 14 potential candidate genes, and we could show, by qPCR, that three of them (YWHAG, E2F1, and TDRD9) differentiated the disease phenotypes CAP, AECOPD, CAP+COPD and healthy.