Given that in transgenic SOD1 models of ALS there is evidence for a shift from alternatively activated to classically activated microglia over the disease course (Gravel et al., 2016; Liao et al., 2012), defining the specific activation state of the cellular source of all the chitinase proteins in CSF will further contribute to understanding of the contribution of neuroinflammation to the clinical heterogeneity of the disease. Here, SOD1 is linked to amyotrophic lateral sclerosis.