Soluble triggering receptor expression on myeloid cells 2 (sTREM2), a microglial marker, and Chitinase-3-like protein 1 (YKL-40), a marker of macrophage activity, as well as chitinase-enzyme activity are increased in AD patients, from preclinical stages, when measured in CSF, but not in plasma [306–311]. This evidence concerns the gene CHI3L1 and Alzheimer disease.