It was recently found that a low plasma concentration of matrix metalloproteinase-9 (MMP-9) is associated with the occurrence of delirium [16], and these proteins have been suggested to be involved in the pathophysiology of brain trauma, leading to an increase in hematoencephalic barrier permeability with exacerbation of posttraumatic edema [17]. The gene discussed is MMP9; the disease is delirium.