CHI3L1 and neurodegenerative disease: In addition, prior studies have shown that CSF levels of YKL-40 are linked to biomarkers of neurodegeneration (total tau, t-tau), damage to large-caliber myelinated axons (NfL), tau-mediated toxicity (p-tau), and synaptic damage (neurogranin, SNAP-25) in various neurodegenerative diseases [89].