MMP9 and early-onset autosomal dominant Alzheimer disease: The ability of MMP-9 to cleave β-amyloid peptide is particularly interesting because an increase in MMP-9 expression was observed in Alzheimer’s disease patients by several research groups (Backstrom et al., 1996; Yan et al., 2006; Mizoguchi et al., 2011a; Filippov and Dityatev, 2012).