Definition:

Parkinson disease (PD) is a progressive neurodegenerative movement disorder that results primarily from the death of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Both environmental factors and mutations in familial PD-linked genes such as SNCA, Parkin, DJ-1, PINK1 and LRRK2 are associated with PD pathogenesis. These pathogenic mutations and environmental factors are known to cause disease due to oxidative stress, intracellular Ca2+ homeostasis impairment, mitochondrial dysfunctions and altered protein handling compromising key roles of DA neuronal function and survival. The demise of DA neurons located in the SNc leads to a drop in the dopaminergic input to the striatum, which is hypothesized to impede movement by inducing hypo and hyper activity in striatal spiny projection neurons (SPNs) of the direct (dSPNs) and indirect (iSPNs) pathways in the basal ganglia, respectively.