CHI3L1 and Alzheimer disease: The results of the age-based subgroup analysis suggested that YKL-40 levels were significantly elevated in the CSF of AD patients with a mean age between 60 and 69 years (SMD = 1.034, 95%CI: [0.689, 1.378]; p = 0.000; Table 3, Figure S6) and between 70 and 79 years (SMD = 0.823, 95%CI: [0.526, 1.121]; p = 0.000; Table 3, Figure S6) than healthy controls.