MMP9 and autism spectrum disorder: MMP-9 serves as a potential disease biomarker in response to various physiological stimuli and pathological insults; the upregulation of MMP-9 enzymatic activity and expression contributes to a wide range of brain disorders, including BBB breakdown, epilepsy, schizophrenia, autism spectrum disorder, brain injury, stroke, neurodegeneration, pain, and brain tumors, among others [10,11].