BDNF and Parkinson disease: The decline in neurotrophic factor levels, particularly brain-derived neurotrophic factor (BDNF) and its receptors, is a well-documented physiological event in neurodegenerative conditions like Alzheimer’s disease (6, 7), Parkinson’s disease (8, 9), multiple sclerosis (10, 11) and amyotrophic lateral sclerosis (12).