YKL-40 is expressed by microglia and astrocytes in the brain and is implicated in the neuroinflammatory response to β-amyloid deposition.45 Elevated CSF YKL-40 is seen in a number of neurodegenerative diseases including prodromal AD,45 as well as in stroke and multiple sclerosis. Here, CHI3L1 is linked to Alzheimer disease.