P4HB and Parkinson disease: This revealed higher levels of PDIA1 (p = 0.096) (Fig. 1a), MANF (p = 0.17) (Fig. 1b), and clusterin (p = 0.31) (Fig. 1c), and reduced levels of PDIA3 (p = 0.27) (Fig. 1d) in PD patients, while GRP78 (p = 0.63) (Fig. 1e) and calreticulin (p = 0.56) (Fig. 1f) levels were similar in both groups.