Initial brain structures accumulating intracellular α-synuclein inclusions are the olfactory bulb, glossopharyngeal, and vagal nerves; then the Lewy pathology spreads to other regions of the brain reaching the amygdala and substantia nigra, where it causes death of dopaminergic neurons consequently leading to the motor symptoms characteristic of PD. This evidence concerns the gene SNCA and Parkinson disease.