Plasma GFAP and plasma YKL-40 concentration were significantly higher in the preclinical AD group based on the Ptau/Aβ1-42 ratio before and after adjusting for covariates age, sex, and APOE ε4 status as these variables also correlated with GFAP, see Fig. 2. The gene discussed is CHI3L1; the disease is Alzheimer disease.