HCN4 and ventilator-associated pneumonia: Swanson et al. in 10 trauma patients that later developed VAP, found that gene expression profiles of lipopolysaccharide stimulated blood cells were different from those expressed in controls who did not develop VAP and showed 5 genes (PIK3R3, ATP2A1, PI3, ADAM8, and HCN4) common to all significant gene sets used in the cross validation tests [30].