In Parkinson disease (PD), the reduction of oligomeric α-syn occurs due to the inhibition of Hsp90 resulting in a lesser cytotoxicity of the mutant A53 α-syn, which leads to increased dopamine [102,108], specifying the Hsp90′s direct interaction with soluble α-syn protein, and the inhibitors of HSP90 stimulate soluble client degradation by UPS before the proteins aggregate (Figure 5). This evidence concerns the gene HSP90AA1 and Parkinson disease.