“My journey thus far fighting this disease has been a lot of education, a lot of reading, and teaching myself how to deal with it. As you know, it affects everyone differently…. I also believe that we must keep it together as much as possible. We must PUSH ourselves.”
—JUDY J., PWP
As of this writing, we still don’t know exactly what causes Parkinson’s. Researchers often theorize that PD is a response to a combination of environmental triggers and genetic factors,14 but no single theory has yet been proven.
Following are several possible causes of PD that researchers are looking into.
Having had a mom with PD means I have been keenly interested in genetics. Does having a close relative with Parkinson’s mean that I will get it too? And if I have kids, will they be at risk as well?
Fortunately for me, the chances are small. While certain genetic variations can cause an inherited form of PD, direct genetic causation accounts for only about 10 percent of Parkinson’s cases thus far. The primary culprit is a gene called LRRK2 (leucine-rich repeat kinase 2), and it is the greatest known genetic contributor to PD (accounting for 1 to 2 percent of all cases).15
Researchers are also studying several other genes and their mutations that may contribute to the disease.16 These include the SNCA (synuclein alpha) gene; the GBA (glucocerebrosidase beta) gene, more common in people of Ashkenazi Jewish descent; and the PRKN (parkin) gene, which commonly contributes to young-onset Parkinson’s disease (YOPD).
You may have heard that digestive issues like constipation are common in people with Parkinson’s; you might experience these yourself and wonder what the heck is going on. A growing body of research now suggests that Parkinson’s disease may be directly related to the health of your gut.
Some of these studies suggest that PD actually begins in the gut, and then navigates to the brain to cause the hallmark Parkinson’s symptoms, like tremors. However, this is just a hypothesis and far from a proven fact. Symptoms may result from certain proteins affecting the vagus nerve that cause nerve cell death if they hit the brain, or from consuming substances that set off inflammatory reactions or alter the composition of healthy bacteria that reside along the gastrointestinal tract.
Whether from a poor diet, a microbiome imbalance, or preexisting condition, if your body isn’t able to fight off the toxins and bacteria that enter your GI system like it used to, then the bad stuff passes right through your gut wall like it’s an open door (when it should be locked to all but the best of guests). After hitting the bloodstream, these bad toxins wreak havoc on your body. This poor gut health leads to, among other things, inflammation, which is also linked to the development and progression of neurological disorders like PD and Alzheimer’s.
So, while there is no exact answer for whether PD begins in the gut or simply reacts to changes within it, it is clear that your GI health and your brain health are connected and should be treated with equal respect. See chapter 46 for a breakdown of the best dietary practices for people with PD.
Studies have shown that being exposed to pesticides may increase a person’s risk for developing Parkinson’s disease. Research from the National Institutes of Health in 201117 showed a link between the use of two pesticides, rotenone and paraquat, and PD. Exposure to either of these pesticides increases the chances of developing the disease by a significant amount. The study revealed that people who had been exposed developed PD 2.5 times more often than those who had not been exposed. Farmworkers who regularly used these pesticides were most at risk. Due to their toxicity, negative effects on the brain, and strong links to Parkinson’s, the usage of both of these pesticides is now largely restricted.
Researchers have been looking into potential links between head trauma, or traumatic brain injury (TBI), and PD for some time. TBI occurs when there is a disruption in the normal function of the brain caused by a bump, blow, or jolt to the head. Many people think of Muhammad Ali and his diagnosis of Parkinson’s being an obvious case for this association. A review of several published studies18 found an association between head trauma and an increased risk of developing PD, and those with a history of head trauma resulting in concussions had an even higher risk.
It is important to note that even though head trauma and TBI are associated with an increased risk of developing PD, researchers warn that this does not mean that head injuries cause the disease. One theory is that TBI is one of many potential environmental factors that may interact with genetics to bring upon a diagnosis of Parkinson’s. Additional research needs to be done to more definitively deem this to be true.
It is possible that occupational exposure to various metals (e.g., copper, lead, and manganese) can be related to the development of Parkinson’s. Researchers have been looking into this, but it’s difficult to measure long-term exposure to metals, and the results of studies measuring PD risk and specific metals have been inconsistent.
For example, people need small amounts of the element manganese to stay healthy. When the dosage gets too high, though, it becomes poisonous. High-dose manganese exposure is known to cause a form of parkinsonism called manganism, which is characterized by feelings of weakness and lack of energy, tremors, a masklike face, and psychological disturbances. Researchers have focused on welders and miners who may have been exposed to high levels of manganese,19 but so far we do not know if this or other types of metals can actually cause Parkinson’s.
Free radicals are atoms in the body that have unpaired electrons. An atom with unpaired electrons will do whatever it can to get those electrons paired off, meaning it is quick to react with things it shouldn’t. The instability of free radicals makes them dangerous: they can damage good cells and create abnormal ones. Fortunately, most of the time the body naturally produces antioxidants to counteract free radicals and detoxify any harmful effects.
Producing a small number of free radicals is normal and manageable. The problem arises when there are too many and the body’s antioxidants can’t keep up. The excess free radicals will do more damage than can be undone. This is called oxidative stress. It is possible that environmental toxins (e.g., pollution, cigarette smoke) may contribute to abnormal free radical formation, thus putting the body into oxidative stress and potentially leading to PD.
Postencephalitic Parkinsonism (PEP)
Around the time of World War I there was a viral disease called encephalitis lethargica that attacked nearly five million people throughout the world, then suddenly disappeared in the 1920s.
PEP became more widely known through neurologist Oliver Sacks’s personal account of his work with PEP patients in a New York hospital in the late 1960s. Titled Awakenings, Sacks’s book explores his use of the then-experimental drug levodopa to temporarily awaken patients trapped in a statue-like state. Today the incidence of PEP has dropped to nearly zero.