CHI3L1 and amyotrophic lateral sclerosis: As an unbiased approach, shotgun proteomics using data‐dependent acquisition (DDA) liquid chromatography–tandem mass spectrometry (LC–MS/MS) has proved itself a powerful tool for biomarker discovery in ALS, identifying an increase in a set of glial proteins—the chitinase proteins chitotriosidase‐1 (CHIT1), chitinase‐3‐like protein‐1 (CHI3L1 or YKL‐40) and chitinase‐3‐like protein‐2 (CHI3L2 or YKL‐39) (Thompson et al., 2018; Varghese et al., 2013).