We used to believe that Parkinson Disease was almost entirely caused by environmental factors. 20 years ago, genetic involvement was deemed to be around 2% of cases or less. Through the advent of advanced and increasingly affordable genetic testing, as well as improved collaboration across the globe, we now believe that genes account for at least 8% of PD, perhaps up to 15% based on more recent data. People with Young Onset Parkinson Disease, those with dystonia early on, and those with symmetric (both sides) findings are probably more likely to have a genetic cause than the more typical patients.
Yes, some environmental factors have been linked to increased risk of PD, such as pesticides, herbicides, fungicides, some heavy metals, and, perhaps, living in North America, but the linkage or direct cause is not as obvious as one might hope. To date, the use of surveys and questionnaires has produced few, if any, clues to the causes of PD.
The virtual revolution that has occurred in genetic testing in the past 20-odd years has allowed us to identify quite a few genes that seem to cause PD, perhaps 15 or 20 genes that are under study, with more being identified at an increasing rate. In a recent interview with Medscape Medical News, Owen A. Ross, PhD, a neuroscientist at the Mayo Clinic said ”The idea that [PD] occurs mostly in a random sporadic fashion is changing.” Dr. Ross was part of consortium of PD researchers who published an online report August 31 in Lancet Neurology. The Genetic Epidemiology of Parkinson’s Disease (GEO-PD) consortium reported the identification of both risk and protective variants in the LRRK2 gene, perhaps the most notorious PD gene both for its dominant inheritance (50% of offspring inherit the gene) and for its association with Sergay Brin, the co-founder of Google who inherited LRRK2 from his mother. Dr. Ross and colleagues found that, while some forms seem to carry increased risk of PD, others may protect against PD to some extent.
Obviously, as in many things, our view of the cause of PD is vastly different than it was just 10 years ago. Hopefully, we will be eventually be able to get a handle on prevention of PD as well as a more satisfying treatment or even a cure.