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Much remains to be discovered about Parkinson's disease, a degenerative neurological condition that affects movement, but research does give us plenty of insight into its risk factors. What should you know?

Parkinson’s disease is a degenerative neurological condition that falls under the "movement disorder" umbrella — meaning, quite simply, that it changes the way in which a person moves. Around a million US residents live with Parkinson's disease, the symptoms of which usually start announcing themselves around age 60. While more and more is known about the risk factors, doctors aren't sure what is behind most individual cases, in which case the disease is referred to as idiopathic Parkinson’s disease. 

What do you need to know about the risk factors?

1. The risk of Parkinson's steadily increases with age

Though the symptoms of Parkinson's disease can manifest earlier (in which case it's deemed to be "early onset" Parkinson's), they typically show up around age 60 — and a person's relative risk of developing the condition continues to rise with age. One percent of people over 60 are thought to have Parkinson's, while five percent of though older than 85 are affected, making increasing age one of the main risk factors

2. Parkinson's is more common in men

Currently available scientific data strongly suggests that Parkinson's disease strikes men more often than women — men are diagnosed with the condition 1.5 times more frequently. This can be explained by a variety of possible factors, including the protective effect the female hormone estrogen seems to offer, the fact that men are more likely to suffer head trauma (another risk factor), differences in environmental exposure to toxins, and even differences in dopamine production — relevant because the brains of people with Parkinson's do not make enough dopamine. Genetic factors may play a role as well, but there's also a possible "human error element". That is, the theory that Parkinson's disease is more common in men remains controversial in some circles, as this impression could, possibly, be due to under-diagnosis in women. 

3. How your ethnicity affects your risk of Parkinson's

Most currently available research suggests that white people have twice the risk of developing Parkinson's disease compared to black and Asian people, while Hispanics (which includes Caucasian and non-Causasian Hispanics) appear to have the highest risk of all.

While nearly all US-based studies into the effect ethnic background has on the risk of Parkinson's disease have similar results, the link between race and Parkinson's disease hasn't been proven beyond reasonable doubt yet. This is because, among other things, knowing which people have Parkinson's depends on diagnosis. Several studies point out that access to (good quality) healthcare and regular medical checkups are necessary to receive a correct diagnosis, and these differences in access may at least partially account for the differences in prevalence found among people of different racial backgrounds, both for socioeconomic and geographical reasons.

4. Can Parkinson's run in families?

The vast majority of Parkinson's patients — 85 percent — do not have known relatives who also suffer from the condition. The remaining 15 percent, meanwhile, have at least one close relative with Parkinson's. This does not mean that Parkinson's disease doesn't have a genetic component, however. Several genetic mutations have been linked to a higher risk of Parkinson's disease, including:

  • Autosomal dominant (one gene mutation). Changes within the Alpha-synuclein (SNCA) and leucine-rich repeat kinase 2 (LRRK2) have been associated with a higher risk of Parkinson's disease (albeit in a very small percentage of those affected), and these particular changes are more likely in males of North African descent. 
  • Autosomal recessive (two copies of the gene mutation must be present).  Genes affected in this case include PARK7, PINK1, and PRKN.
  • Modifier genes of disease expression. The gene GBA, which produces an enzyme called glucocerebrosidase, is one of the genes that influences a person's odds of Parkinson's without leading to symptoms .

While genetic mutations can increase a person's risk of developing Parkinson's disease, they do not guarantee that the disease will occur. If you do happen to have a family history of Parkinson's, you can talk to your doctor about the possibility of genetic screening, but its results will not necessarily give you the answers you are looking for. 

5. Does a history of head trauma lead to Parkinson's? 

Just one incident of head trauma may, research suggests, increase your risk of Parkinson's disease. A study of combat veterans indicated that a mild traumatic brain injury is all it takes to boost a person's odds of developing the condition by more than 50 percent, a conclusion its authors came to after controlling for psychological factors and other things that may increase risk. 

The long-term risks of concussion have been a hot topic in the sports world for some time now, and the risk of Parkinson's only adds to that. Whether to protect against Parkinson's or the other potential consequences of head trauma, anyone engaging in any kind of activity that carries a significant risk of head trauma should wear protective gear (seatbelts or headgear, for example) — and promptly get themselves to a doctor if they do suffer an injury.

6. What role do environmental factors play?

Studies that explored the possible connection between neurological disorders including Alzheimer's and Parkinson's disease and environmental exposure to pesticides have reached contradictory results — some studies found a correlation while others did not. Along with pesticide exposure, drinking well water and even living in the countryside have both been proposed to increase a person's risk of ending up with Parkinson's disease. There's no evidence that this is true, however, as urban dwellers actually have the condition in higher numbers.

7. What about chemicals and metals? Could Parkinson's be an occupational risk?

Workers exposed to certain chemicals and metals over the course of their career  — pesticides again, but also herbicides (paraquat), fungicides (maneb), and insecticides (rotenone) — could, research suggests, be more likely to develop Parkinson's. Vietnam vets who were exposed to Agent Orange may likewise be at a higher risk, though research is inconclusive. 

Long-term exposure to large quantities of the metals mercury, lead, iron, copper, manganese, thallium, zinc, aluminum, and Bismuth was, again, linked to a higher incidence of Parkinson's, along with the solvent Trichloroethylene (TCE) that is also found in groundwater and polychlorinated biphenyls (PCBs). 

8. Will your medications predispose you to Parkinson's disease?

The long-term use of certain medications may be linked to an increased risk of Parkinson's disease:

  • Antidepressants
  • Anxiolytics (anti-anxiety drugs)
  • Hypnotics
It is not currently clear why, but your medications themselves may not actually be to blame — a history of depression, the treatment of which may involve any of these medications, may also explain the link.

9. Synthetic heroin: Don't do it

MPTP, a synthetic, heroin-like, opioid drug, has been shown to cause irreversible Parkinsonism — symptoms of Parkinson's disease — by destroying neurons related to dopamine production. These symptoms can, research reveals, appear even after taking the drug a few times. The moral of this particular story is, as always, "don't do drugs", but the Parkinson's-like symptoms seen in young drug abusers may also lead to very interesting insights into the mechanism through which Parkinson's disease develops.

  • Xu, Y., Yang, J., & Shang, H. (2016). Meta-analysis of risk factors for Parkinson’s disease dementia. Translational Neurodegeneration, 5(1). doi:10.1186/s40035-016-0058-0
  • Hubble, J. P., Cao, T., Hassanein, R. E. S., Neuberger, J. S., & Roller, W. C. (1993). Risk factors for Parkinson’s disease. Neurology, 43(9), 1693–1693. doi:10.1212/wnl.43.9.1693
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