MAPT and Alzheimer disease: Several studies have shown that patients with AD have a higher MMP-9:TIMP-1 ratio and a lower level of TIMP-1 in the cerebrospinal fluid (CSF) compared with cognitively healthy elderly individuals, and the MMP-9:TIMP-1 ratio in patients with AD correlates with T-tau in the CSF, a marker of neuronal degeneration [188].