The presence of the risk allele, Rep1-261 bp, of the dinucleotide repeat polymorphism in the promoter of SNCA leads to an increase of alpha-synuclein expression in vitro and in vivo (Chiba-Falek and Nussbaum 2001; Cronin et al. 2009), leading to increased protein levels in blood of PD patients carrier of this variant compared to the protective genotype (Fuchs et al. 2007). This evidence concerns the gene SNCA and Parkinson disease.