MMP9 and hyperhomocysteinemia: We have demonstrated the role of proteinase/convertase and anti-proteinase in the accumulation of homocysteine (Hcy, i.e., hyperhomocysteinemia (HHcy)) by the disrupted folate-1 carbon metabolism (FOCM) cycle; in vascular stiffness [15], contributing to the enlarged perivascular space (EPVS) [17,18,19,20]; and in vascular contributions to cognitive impairment and dementia (VCID) via the activation of matrix metalloproteinase-9 (MMP-9) [21,22,23].