What Causes Parkinson's Disease?

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Parkinson’s disease (PD) occurs when brain cells that make dopamine, a chemical that coordinates movement, stop working or die. The dopamine-generating cells are in the substantia nigra, a region of the midbrain. Dopamine is the chemical that sends messages to the part of the brain that controls movement and coordination.  The loss of dopamine causes neurons to fire without normal control, leaving patients less able to control their movement.  PD can cause tremor, slowness, stiffness, and walking and balance problems. But constipation, depression, memory problems and other non-movement symptoms also can be part of Parkinson’s. PD is a lifelong and progressive disease, which means that symptoms slowly worsen over time.

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Researchers believe that in most people, Parkinson's is caused by a combination of environmental and genetic factors. Certain environmental exposures, such as pesticides and head injury (think of Muhammad Ali), are associated with an increased risk of PD. Still, most people have no clear exposure that doctors can point to as a straightforward cause. The same goes for genetics. Although genetics may be a contributing factor, the majority of Parkinson’s cases are not genetically related. You have a slightly higher risk of getting PD if you have a parent or sibling with Parkinson’s; about 15% of individuals with PD have a first-degree relative who has the disease.

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Aging is the greatest risk factor for Parkinson’s.  The average age at onset is 60, but people have been diagnosed as young as 18.  Men are diagnosed with Parkinson’s at a slightly higher rate than women but PD does not discriminate based on race. Researchers are studying these disparities to understand more about the disease and health care access and to improve inclusivity across care and research. 

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