MMP9 and early-onset autosomal dominant Alzheimer disease: Experiments have demonstrated that matrix metalloproteinase-9 (MMP9) is involved in the processes of neuroinflammation and neuronal damage in Alzheimer’s disease (AD) by degrading the integrity of the blood-brain barrier (BBB), promoting amyloid-beta (Aβ) deposition, and exacerbating tau protein pathology.