Most cases of Parkinson’s disease are idiopathic, which means that the cause is not clear.
It is widely believed that a person with Parkinson’s disease may be genetically susceptible to the disease and that one or more unknown factors in the environment ultimately lead to it.
Most of the symptoms of Parkinson’s disease come from a loss of nerve cells in an area of the brain called the substantia nigra. (7)
Normally, neurons in this part of the brain make the chemical messenger dopamine (neurotransmitter), which allows communication with another region of the brain, the striatum.
This connection helps produce smooth, purposeful motion. When neurons in the substantia nigra die, the resulting loss of connectivity leads to the motor symptoms (related to movement) of Parkinson’s disease. (8)
Although the cause of this cell death is not known, many researchers believe that the cells are killed by clumping proteins called Lewy bodies. (8)
What are Lewy bodies?
The affected neurons of people with Parkinson’s disease have been found to contain clumpy proteins called Lewy bodies. (9) Researchers are not yet certain why Lewy bodies form or what role they play in disease, but it is believed that Lewy bodies are toxic. (9)
Lewy bodies are clumps of a protein called alpha-synuclein. Neurons cannot break down the protein clumps, which can lead to these cells dying. (9)
Some other theoretical causes of brain cell death in people with Parkinson’s disease include free radical damage, inflammation, or toxins.
Learn more about Lewy body dementia
What are the risk factors for Parkinson’s disease?
Risk factors for Parkinson’s disease include:
People who have a first-degree relative (parent or sibling) with Parkinson’s disease are at an increased risk of developing the disease – perhaps 9 percent greater. Genetic risk factors (the presence of certain genes associated with Parkinson’s disease) appear more commonly at the onset of Parkinson’s disease.
Fifteen percent of people with Parkinson’s disease have a known relative with the disease, but a condition called familial Parkinson’s, which has a known genetic link, is relatively rare. (10)
The average age of onset is 60 years, and the incidence increases with age. About 4 percent of people have “premature onset” or “early onset” disease, which begins before the age of 50. (11)
Parkinson’s disease affects 50% more men than women for unknown reasons. (12)
Exposure to pesticides
Exposure to certain pesticides has been shown to increase the risk of developing Parkinson’s disease.
Problem chemicals include organochlorine pesticides such as DDT, dieldrin, and chlordane. Rotenone and permethrin are also implicated. (13)
Exposure to fungicides and herbicides
Exposure to the fungicide or herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), paraquat, or Agent Orange may increase the risk of Parkinson’s disease.
The U.S. Department of Veterans Affairs considers Parkinson’s disease to be a possible service-related illness if a person is exposed to large amounts of Agent Orange. (14)
Repeated head injuries, especially recurrent head injuries, may contribute to the development of Parkinson’s disease in some people. (15)
Coffee and smoking
People who drink coffee or smoke tobacco in moderation have been found to have a lower risk of developing Parkinson’s disease, for reasons that are still unclear. (16) But while smoking can reduce the risk of Parkinson’s disease, it clearly increases the risk of lung cancer and cardiovascular disease, including heart attack and stroke.