BDNF and Parkinson disease: However, the alterations in BDNF levels in CSF and blood in PD patients as reported in multiple studies are complex and inconsistent, and its biomarker potential in this disorder is not established (Nagatsu et al., 2000; Salehi and Mashayekhi, 2009; Ventriglia et al., 2013; Jiang L. et al., 2019).