In vitro study, IL-6 causes neuronal cell death (Conroy et al., 2004), and both consecutive low doses (5 × 10 ng/ml) and a single high dose (50 ng/ml) of IL-6 can increase the expression of PD-related protein, α-synuclein (Bick et al., 2008). This evidence concerns the gene IL6 and Parkinson disease.