CHI3L1 and Alzheimer disease: Consistent with the significant elevation of Aβ1–42, the serum levels of CHI3L1 in AD patients were significantly elevated (29.5 ± 0.7 ng/mL) compared to that of healthy controls (16.2 ± 0.7 ng/mL) (n = 25, p < 0.001) (Figure 1A).