YKL-40, a chitinase expressed by astrocytes and microglia in the CNS [8], was increased in the CSF of Aβ+ CN individuals and patients with AD, and negatively associated with thickness measures in AD-vulnerable brain regions, replicating prior findings [2] and reemphasizing similar findings from the same cohort, using a standard ELISA assay [19]. Here, CHI3L1 is linked to Alzheimer disease.