MMP9 and early-onset autosomal dominant Alzheimer disease: A second study found that 79% of CAA-affected vessels were immunopositive for MMP-9 in CAA cases with (n = 4) and without (n = 6) Alzheimer disease (AD), while only 5% of control vessels were immunopositive for MMP-9 (n = 4 non-CAA control cases).