Pro-inflammatory M1 microglia, induced by a persistent stimulus (e.g., misfolded alpha-synuclein in PD), produces a significant number of nitric oxide (NO) and pro-inflammatory cytokines, such as interleukin 1beta (IL-1β) and tumor necrosis factor (TNF-α), and these neurotoxic factors could cause neuronal damage in PD (Song et al., 2018). This evidence concerns the gene SNCA and Parkinson disease.