P4HB and amyotrophic lateral sclerosis: In line with this is the finding of PDIA1 levels being upregulated in the cerebrospinal fluid (CSF) of ALS patients (Atkin et al., 2008) and a study exposing spinal MNs to CSF of ALS patients documented an induction of ER stress in the MNs (Vijayalakshmi et al., 2011).