CHI3L1 and Alzheimer disease: Compared to HC (226 ± 82 pg/mL), YKL-40 levels were significantly increased in sCJD (411 ± 157 pg/mL, p < 0.001) and AD (311 ± 113 pg/mL, p < 0.01) (Fig. 8a, cohort 2 Additional file 2).