While several biomarkers of vascular dysfunction have been identified in relation to AD, prior studies suggest that matrix metalloproteinase-9 (MMP-9) may be particularly relevant to AD pathophysiology, due to its interaction with the apolipoprotein ε4 allele (APOE ε4) [4], the major genetic risk factor for sporadic AD, and its involvement in neuroinflammation [5], amyloid-β (Aβ) brain metabolism [6], and blood-brain barrier breakdown [7]. This evidence concerns the gene MMP9 and Alzheimer disease.