Particularly, genetic polymorphisms in the SNCA gene have been consistently associated with PD risk in genetic association studies and subsequently replicated in large-scale GWAS, including a dinucleotide repeat sequence (Rep1) within the promoter region and several single nucleotide polymorphisms (SNPs) at the 3′end of the gene, overall suggesting that SNCA alleles associated with increased disease risk correlate with higher α-synuclein expression, and pointing to a gene dosage effect [52–60]. This evidence concerns the gene SNCA and Parkinson disease.