In contrast, several biomarkers—including CHIT1, CXCL-12, IgG, and the ratio of neurofilament light (NfL) to YKL-40, as well as soluble APPβ to YKL-40—were significantly lower in CSF in FTD relative to ALS [36,72,102]. This evidence concerns the gene CHI3L1 and amyotrophic lateral sclerosis.