http://www.journalofparkinsonsdiseas...mans_Blog.html

excerpt

In a sense, in this paradigm every parkie has his/her own version of the disease. This picture makes perfect sense to epidemiologists and geneticists. For example, Parkinson’s Institute’s Caroline Tanner says, “the combination of genetics and environment is central to understanding PD etiology…Take head trauma as a risk for PD… By itself, concussions might be a small risk factor for PD, but when combined with a genetic predisposition – a variant in the alpha-synuclein gene that has a tiny effect in people without head injury – the risk increases 11-fold.”


But what does it mean for therapies? For one thing, it makes clinical trials much more complicated. As Haydeh Payami, Professor of Molecular Genetics at the New York State Department of Health Wadsworth Center put it, “for any given drug there are some responders and some people who do not respond, and the non-responders dilute the effect of a drug.”