Is believed to be in mutations of "superoxide dismutase" (have some fun, google it and read al about it) . It is not a stretch of the imagination to think that certain cells are more sensitive to oxidative damage, like nigral neurons, which have ben shown to be destroyed in vivo, by the selective uptake of certain toxins, and their subsequent oxidative metabolism to a toxin which disturbs the electron chain mechanisms that occur in the mitochondria, which eventually cause cellular death. Too much iron , just like too much manganese, around in the cellular environment, if present in an oxidation state where it can interfere with the normal cellular respiration, may be at the root of the destruction of certain cells, that result in the expression of disease. This has been speculated for a long time, but such things are difficult to transfer in to disease prevention and control. Be wise, take antioxidants, but don't overdo it. Always be aware of what you are putting into your body, otherwise, harm may replace any benefit. Get the facts about anything by doing a simple net search, but don't trust sites that recommend the use of any specific product, there are supplements which are not beneficial, and there are drugs which are harmful or not useful for parkinsons, including FDA approved formulations.