Scientists believe a combination of genetic and environmental factors are the cause of Parkinson’s disease (PD). PD is an extremely diverse disorder. While no two people experience Parkinson’s the same way, there are some commonalities. PD affects about one million people in the United States and ten million worldwide. The main finding in brains of people with PD is loss of dopaminergic neurons in the area of the brain known as the substantia nigra.
In December, two reports in the New York Times called attention to the potential link between paraquat, a strong pesticide, and Parkinson’s disease (PD). The pesticide, which has been previously linked to Parkinson’s, is banned in some countries including those where it is manufactured, but not in the US.
What should people with Parkinson’s know about this news?
There has long been a fascination about the relationship between welding, mining and Parkinson-like symptoms. In this month’s What’s Hot blog and in my NEJM Journal Watch blog I explore this murky history and relationship. Doctors and health care professionals long ago identified a Parkinson-like syndrome that developed in welders and manganese miners. Manganese, the chemical, has been linked to Parkinson-like symptoms (also referred to as parkinsonism). Manganese exposure related to parkinsonism symptoms dates back to the late 1960s and early 1970s.
Welders exposed to fumes containing low levels of the metal manganese had a high rate of Parkinson-like symptoms, which progressed with increasing cumulative exposure to the metal, according to research published in the December 28 online edition of Neurology. The results make a case for better worker protection. They also help scientists understand the underlying mechanisms by which exposure to substances in the environment may contribute to Parkinson’s disease (PD).
A French group presented data at the 20th International Congress of Parkinson’s Disease and Movement Disorders in Berlin Germany last month. Their results suggested a strong link between farming, pesticides and risk of Parkinson’s disease. Sofiane Kab and her colleagues demonstrated that living in rural French regions with more crops was a high risk for the later developing Parkinson’s. The authors noted that these are typically regions where vineyards are located.
There has long been speculation that viral infection may cause dopamine responsive Parkinson’s disease — at least in a subset of patients. The most famous case examples were depicted in the 1990 movie Awakenings starring Robin Williams and Robert De Niro (based on Oliver Sacks’ 1973 memoir) where Parkinsonian patients (presumed to have been suffering from a viral flu or sleeping sickness) awaken when exposed to dopamine. Though more common viruses have been considered as potential Parkinson’s disease triggers, there has been a lack of evidence to support this notion.
There are many great mysteries and unanswered questions surrounding the potential causes of Parkinson’s disease. One of the most important and most studied is, “why are only a minority of cases caused by a single genetic abnormality?” One famous researcher from California coined the phrase, “the genes load the gun, and the environment pulls the trigger” (Judith Stern, UC Davis). Many Parkinson’s disease researchers have refocused their efforts to attempt to identify potential environmental triggers.
The recent publication, in the American Journal of Epidemiology, addressing metal emission and urban incidence of Parkinson’s disease (PD) underscores the public’s growing concern that manganese, copper, and other metals may play a role as an environmental cause of Parkinson’s disease. Willis et. al.
Pesticides, Agent Orange, and potential environmental risk factors for the development of Parkinson’s disease (PD) continue to make the news. Patients and families may be comforted by headlines on chemicals and Parkinson’s, most of which they may never be exposed to. The recent report by Goldman and colleagues from the Parkinson’s Institute, a Parkinson'a Foundation Center of Excellence in Sunnyvale, CA, may open some eyes to environmental exposures and Parkinson’s disease risk.