For instance, apoE4 displayed a weaker ability to inhibit the function of matrix metallopeptidase 9 (MMP-9) than apoE2 or apoE3, given that MMP-9 expression and activity was elevated in the cerebrovasculature of both human and animal AD brains from specimens with the APOE ε4 genotype [71]. Here, MMP9 is linked to Alzheimer disease.