The commonly held view is that early in MS pathogenesis, BBB integrity is compromised when inflammatory leukocytes release proteolytic enzymes such as matrix metalloproteinase (MMP)-9 which digest ECM components of the vascular basement membrane as well as tight junction proteins connecting endothelial cells tightly together, to effectively punch holes in the BBB [2, 32, 40]. The gene discussed is MMP9; the disease is myeloid sarcoma.