CHIT1 and amyotrophic lateral sclerosis: Using the 12 most differentially abundant proteins (CHI3L1, TMEM198, CHIT1, CHI3L2, HYOU1, XXYLT1, DPP6, C1QB, FABP5, MERTK, UCHL1, and WARS), PCA effectively distinguished ALS from controls (Fig. 7a).