The development of biomarkers for amyotrophic lateral sclerosis (ALS, the commonest phenotype of MND) is a priority to reduce diagnostic delay, allow earlier assessment of therapeutic activity, and provide pathogenic insight.
Liquid chromatography tandem mass spectrometry with label-free quantification was used to quantify CSF proteins in individual participant samples. A longitudinal cohort comprised patients with ALS (n=43) and primary lateral sclerosis (PLS, n=6). A cross-sectional cohort comprised healthy (n=20) and disease control patient CSF samples (Parkinson’s disease n=20, MND mimic disorders n=12).
Among 773 identified proteins, significantly elevated levels of three macrophage-derived chitinase proteins were detected in the ALS group, specifically chitotriosidase (CHIT1), chitinase-3-like protein 1 (CHI3L1) and chitinase-3-like protein 2 (CHI3L2). Levels correlated with rate of disease progression (CHIT1 r=0.56, p<0.001; CHI3L1 r=0.31, p=0.028; CHI3L2 r=0.29, p=0.044), and levels of the axonal degeneration marker phosphorylated neurofilament heavy chain (r=0.62, p<0.001; r=0.49, p<0.001; r=0.41, p<0.001). Levels of CHI3L1, but not CHIT1 or CHI3L2, increased over time in those with low initial values (gradient=0.005 log abundance units/month, p=0.001).
Microglial activation has been implicated in the pathogenesis of MND and neuroinflammatory pathways are a major target of therapeutic interest. CSF chitinases may be potential pharmacodynamic as well as diagnostic biomarkers.