CoQ-10 is a conditionally essential anti-oxidant vitamin that is required for mitochondrial function.
Statin drugs suppress the body's ability to make CoQ-10, so supplementation is especially important for persons taking statin drugs.
Coenzyme Q10 has been shown to inhibit the formation of α-synuclein fibrils and to destabilize estabilized preformed fibrils in a dose-dependent manner. [Ono K, Yamada M. Vitamin A potently destabilizes preformed alpha-synuclein fibrils in vitro: implications for Lewy body diseases. Neurobiol Dis Feb 2007;25(2): 446-454].
In a small trial, high dose CoQ-10 has been shown to slow the progression of Parkinson's disease by 40%. However, these high doses are extremely expensive.  Shults CW, Oakes D, Kieburtz K, et al. Effects of coenzyme Q10 in early Parkinson disease: evidence of slowing of the functional decline. Arch Neurol Oct 2002;59(10): 1541-1550.]  Shults CW, Flint Beal M, Song D, and Fontaine D. Pilot trial of high dosages of coenzyme Q10 in patients with Parkinson's disease. Exp Neurol Aug 2004;188(2): 491-494.]