No one knows exactly what causes Parkinson's disease, but it could be the result of your age, environment, genetics, and other factors.

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Parkinson's disease is caused when the brain cells responsible for producing dopamine, the chemical messenger that coordinates the body's muscle movements and emotional responses, stop working or die. It typically leads to motor symptoms such as tremor, stiffness, and slowness of movement (known as bradykinesia). It can also lead to other symptoms such as anxiety and depression. 

Parkinson's Disease Causes

But despite understanding a lot about the symptoms of this disease, one big question still remains: What causes Parkinson's disease?

Unfortunately, there's not a simple answer for that. "We don't have one cause," Lynda Nwabuobi, MD, assistant professor of clinical neurology at Weill Cornell Parkinson's Disease and Movement Disorders Institute, tells Health. "But based on what we have studied and learned, we know Parkinson's disease happens due to an interaction between the aging brain, your genetics, and your environment." 

Here, with the help of doctors, we take a closer look at some of the things that may cause Parkinson's, or increase your risk for the neurodegenerative disorder.

Age 

Age doesn't directly cause Parkinson's disease, but "being an older person" is the greatest risk factor for the neurological disorder, says Dr. Nwabuobi. Why? One explanation is that brain cells are more prone to injury over time, just like the rest of the human body. Another is that gene expression—essentially the way a person's genes operate—can morph over time, triggering changes in cellular activity that ultimately lead to Parkinson's. 

Usually, people with Parkinson's are diagnosed in their 60s and the likelihood increases with age. But there's always the possibility that someone develops early-onset Parkinson's, or Parkinson's that occurs before the age of 50. In those cases, which represent an estimated 4% of the diagnosed population, the disease is more likely to be linked to genetics.  

Genetics 

According to the Parkinson's Foundation, genetics cause Parkinson's in about 10% to 15% of cases. But genetic research is still in its infancy, so experts don't have a full picture of the role genes play just yet. "Many gene mutations have been found, but we know that we're just touching the surface," Dr. Nwabuobi says.

Researchers at the National Institutes of Health made the first connection between genetics and Parkinson's in 1997, finding that mutations in the SNCAgene (PARK 1), which makes the protein alpha-synuclein, were linked to the disease. Specifically, they found that in brain cells of people with Parkinson's, alpha-synuclein gathers in clumps called Lewy bodies. (These clumps are also associated with Lewy body dementia, the disease Robin Williams was diagnosed with after his death in 2014.)

Then there's the GBA1 mutation, which has recently emerged as the most common genetic abnormality linked to PD. Normally, the GBA1 gene produces GCase, a protein that essentially clears out unwanted cells (think of it as a garbage disposal). But when GBA1 is out of whack, it allows for a buildup of alpha-synuclein, which may potentially be a clue for the cause of Parkinson's disease.

Another mutation associated with Parkinson's can occur in the LRRK2 gene. In fact, there are at least 20 known LRRK2 mutations, according to the Parkinson's Foundation, and they can be found in up to 2% of all people with Parkinson's. Individuals who are of Ashkenazi Jewish and North African Berber descent are particularly prone to this gene mutation. 

Does that mean that someone whose parent has Parkinson's is definitely going to develop the disease? No. "Even when someone has a gene mutation associated with Parkinson's, the likelihood of developing the disease is low," according to the Parkinson's Foundation. 

But the presence of a gene mutation could play a considerable role in the cause of Parkinson's—and there's an enormous push to advance research on genetics in order to better understand the disease, improve treatment and, hopefully, discover a cure. 

"What we don't know is much more than what we do know," Dr. Nwabuobi says. "I encourage everyone to get genetic testing, especially patients who have a family history. The more people we test, the more we discover."

Environment and lifestyle

The environment in which you live your life can also potentially cause Parkinson's, or increase your risk for it.

What is your occupation? Where do you live? Have you been exposed to any toxins? Although experts haven't pinned down the exact link between such environmental factors and the cause of Parkinson's disease, evidence suggests they may play a role in the development of the disease. 

"There are certain toxins that have been shown to increase risk of Parkinson's," Dr. Nwabuobi says. "For example, Agent Orange, which many veterans were exposed to in Vietnam."

Likewise, certain metals, herbicides, or fungicides could also increase your risk of Parkinson's. According to the Parkinson's Foundation, the herbicide paraquat is of particular concern—and despite being banned in 32 countries, including the European Union and China, it's still widely used in the United States.

Researchers have also been exploring whether traumatic brain injuries or concussions can cause Parkinson's disease. Research shows that having just a single concussion can increase the risk of Parkinson's disease by 57%.

"If you're a football player or a boxer and you've had multiple concussions," Dr. Nwabuobi says, "that increases your risk." 

Medications and Parkinson's symptoms

Taking certain medications—specifically ones that block the action of dopamine—could cause Parkinson's disease symptoms. It's a condition called drug-induced parkinsonism, and while it isn't Parkinson's disease itself, it can look and feel a lot like it.

Here are some of the drugs can cause Parkinson's disease symptoms:

  • Antipsychotics (like fluphenazine, pimozide, haloperidol, and perphenazine)
  • Anti-nausea medications (including chlorpromazine, droperidol, and promethazine)
  • Drugs that treat hyperkinetic movement disorders (such as tetrabenazine, deutetrabenazine, and valbenazine)

Keep in mind that even though these medications (and others) could cause symptoms similar to Parkinson's, they don't cause the disease itself. And most of the time, the symptoms go away within hours or days once you stop taking that drug, per the Parkinson's Disease Society.

In some cases, the Parkinson's symptoms don't go away after a person stops taking the medication that led to them, and they're eventually diagnosed with Parkinson's disease.

Researchers don't think that the medication was the cause of Parkinson's in those cases, but that those individuals' dopamine levels were already depleted, and the side effects of the drugs revealed their underlying Parkinson's disease. Put another way, the medication was the "straw that broke the camel's back," according to the American Parkinson Disease Association.

Research on what causes Parkinson's disease continues to grow. If you experience symptoms of Parkinson's, such as a tremor, slowed movement, balance problems, or changes in your speech or writing, connect with a doctor to diagnose the condition.

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