CHIT1 was identified in CSF using mass spectrometry and found to be a candidate prognostic marker.63,64 A longitudinal mass spectrometry analysis indicated that CHIT1, CHI3L1 and CHI3L2 correlate with disease progression and with pNfH levels.66 Using commercially available ELISAs, Gille et al. 59 showed that CHIT1 and CHI3L1 poorly discriminate between ALS and mimics and weakly correlate with disease progression. Here, CHI3L1 is linked to amyotrophic lateral sclerosis.