Cerebrospinal fluid levels of YKL-40 in prodromal Alzheimer’s disease

•The underlying mechanism of apolipoprotein E (APOE) ε4 in the pathogenesis of AD remains elusive.•The results indicated that APOE ε4 might affect CSF YKL-40 in MCI subjects. Recently, cerebrospinal fluid (CSF) YKL-40 levels were reported to be a promising candidate biomarker of glial inflammation in Alzheimer’s disease (AD). To detect how APOE ε4 affects CSF YKL-40 levels in cognitively normal (CN) states, mild cognitive impairment (MCI) and AD dementia, data from 35 CN subjects, 63 patients with MCI, and 11 patients with AD from a cross-sectional study in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database were investigated. The results showed that CSF YKL-40 concentrations were increased in the AD dementia group than in the CN group. CSF YKL-40 levels were higher in APOE ε4 carriers than in noncarriers with MCI. No statistically significant difference was found in CSF YKL-40 levels between APOE ε4 carrier and noncarriers in AD and CN subjects. CSF YKL-40 concentrations were tightly related to CSF tau and p-tau concentrations in the MCI group. Analysis implied that APOE ε4 might affect CSF YKL-40 levels in MCI subjects, suggesting a crucial role of APOE ε4 in neuroinflammation in detecting individuals who might convert to AD from MCI and, thus, as an effective predictive factor.