The possible reasons are: (1) Levels of YKL-40 in CSF are increased in stroke, multiple sclerosis, amyotrophic lateral sclerosis, and other neurological disorders [28–31], indicating that it is not specific to AD but instead seems to be a more common marker for inflammation; (2) the sample size of this study is small, especially in the AD group. This evidence concerns the gene CHI3L1 and nervous system disorder.