BDNF and Parkinson disease: BDNF expression is decreased in many neuropsychiatric and neurodegenerative diseases, including depression, bipolar disease, schizophrenia, Alzheimer’s disease, HD, SCA6 and Parkinson’s disease (Ferrer et al., 2000; Zuccato and Cattaneo, 2007; Takahashi et al., 2012; He et al., 2013; Shin et al., 2015).