BDNF and Parkinson disease: Spearman's correlation test indicated moderate and significant opposite correlations between TFAM, BDNF, FNDC5 and miR‐193b expressions in PD PBMCs (r = −.6602, P = .0015/ r = −.5128, P = .0208/ r = −.6015, P = .0050, respectively) (Figure 7B‐D).