One of the most important mechanisms of the pathogenesis of PD is the inhibition of α-synuclein degradation by the ubiquitin–proteasome system in neurons, which is accompanied by the accumulation of α-synuclein and its transformation into oligomeric complexes that are toxic to neurons, especially to dopaminergic neurons of the nigrostriatal system [85,86,87,88]. Here, SNCA is linked to Parkinson disease.