Abnormal levels of alpha-synuclein are common to several neurodegenerative diseases (e.g., Lewy body disease, multiple system atrophy, PD), suggesting that aggregation of this protein is particularly neurotoxic and exacerbates neuronal degeneration (Yang et al., 2018; Parnetti et al., 2019). This evidence concerns the gene SNCA and neurodegenerative disease.