MAPT and Alzheimer disease: Our findings on YKL-40 agree with previous data showing increased CSF levels of this protein in preclinical, prodromal, and dementia stages of AD.21, –, 24 A recent meta-analysis confirmed elevated levels of YKL-40 in AD dementia, although the association with AD was moderate compared with the core CSF AD biomarkers Aβ42, t-tau, and p-tau.25 Earlier studies have indicated that CSF YKL-40 is associated with tau pathology, since it may identify individuals with abnormal tau levels in CSF.21,26