CHIT1 and amyotrophic lateral sclerosis: In particular, recent studies have revealed that chitotriosidase (CHIT1), chitinase-3-like protein 1 (YKL-40, or CHI3L1), and chitinase-3-like protein 2 (YKL-39, or CHI3L2) demonstrate a significant increase in their concentrations in the CSF of ALS patients compared with mimicking conditions [292, 293].