We hypothesize that the 3′ signal is important for the level of SNCA expression and the initiation of the Parkinson’s disease process, particularly in subcortical areas, whereas the 5′ SNP is associated with the expression of SNCA in the cortex.49 Indirectly, this suggests that local SNCA expression is important, distinct from cell to cell spread from subcortical areas. This evidence concerns the gene SNCA and Parkinson disease.