MMP9 and Alzheimer disease: Moreover, the expression of MMP9 is elevated in several neurological conditions, including ischemia, neurodegenerative diseases (e.g., Parkinson’s, Huntington’s, and Alzheimer’s diseases), ASDs, Fragile X syndrome [32,49,64,65], and in neuroinflammatory disorders such as multiple sclerosis, for which MMP9 has been proposed to have a pathogenetic role in the disruption of the BBB [49].