Expression of matrix metalloproteinase (MMP) in healthy brain is relatively low, but activated MMPs, especially MMP-2 and MMP-9, increase during stroke, which leads to disruption of blood brain barrier (BBB) integrity and contributes to brain edema (Machado et al., 2006; Rosenberg and Yang, 2007; Lenglet et al., 2014). The gene discussed is MMP9; the disease is Stroke.