Recent findings from animal studies have suggested that α-synuclein expression level correlates with neuronal vulnerability in PD [30, 35]; likewise, in our model, higher regional abundance of normal α-synuclein agents should indicate greater likelihood of exposure to and growth of infectious agents, higher chance of disease transmission, and, consequently, greater vulnerability to the accumulation of misfolded α-synuclein. This evidence concerns the gene SNCA and Parkinson disease.