The addition and inhibition of CXCL12 in our plasma exposure experiments supports a causal role for CXCL12 in age-related endothelial dysfunction, as inhibition of CXCL12 in old vehicle plasma improved endothelial responses and adding exogenous CXCL12 to young plasma induced endothelial dysfunction. The gene discussed is CXCL12; the disease is endothelial dysfunction.