Genetically, SNCA (α-synuclein gene) duplications, SNCA Rep1 microsatellites, and SNCA polymorphism contribute to the cognitive impairments and dementia in PD [15–20], and DYRK1A polymorphisms, which encode a kinase that phosphorylates α-synuclein, are associated with dementia in PD [21]. This evidence concerns the gene SNCA and Parkinson disease.