SNCA and Parkinson disease: Direct evidence of a relationship between elevated α-synuclein and human parkinsonism was originally provided by genetic studies showing parkinsonian symptoms as well as PD-like pathology (including nigrostriatal neurodegeneration and accumulation of α-synuclein inclusions) in individuals carrying multiplication mutations of the α-synuclein gene (SNCA) and displaying enhanced α-synuclein brain expression at both the RNA and protein levels [27, 28].