Genetic variants that increase the risk of Parkinson’s disease

Parkinson’s disease is a neurological disorder caused by the degradation of dopamine-producing neurons in a part of the brain called the substantia nigra. It affects up to 10 million people worldwide. Symptoms of Parkinson’s include a tremor (usually in the hand), problems with balance and walking, problems with moving limbs, and, for some, depression, sleep problems, and dementia. Loss of the sense of smell is often an early symptom that may happen several years before any of the motor symptoms.[ref]

Causes of Parkinson’s Disease:

Parkinson’s disease (PD) is not yet fully understood. Researchers think that it is caused by a combo of genetics and environmental factors.  For early-onset Parkinsons, there are several genetic mutations that are thought to cause it, but this type of PD only affects about 10% of patients.

Environmental Causes

Environmental causes of PD (that probably combine with genetic susceptibility) include exposure to certain toxins.[ref] Paraquat is an herbicide that has been linked to increasing the risk for PD.[ref] It is still in use in the US, but the EU banned it in 2007. Maneb is fungicide that is also linked to PD. It is often used to create Parkinson’s in animal research. Mancozeb is another formulation of maneb, and it is sold under a variety of brand names and used for potato blight, downy mildew on grapes, and other plant fungal diseases.

Trichloroethylene (aka trichlor) is another chemical that is linked to PD.[ref] It is an industrial solvent and used to be used in refrigerants. Initially, trichloroethylene was used as an anesthetic as an alternative to ether and chloroform. But better anesthetics have come along, and trichloroethylene had a bad side effect of cardiac arrhythmia and neurologic dysfunction.  It is now listed by the EPA as having both carcinogenic and non-carcinogenic health effects. The main route of exposure is contaminated drinking water in areas near industrial spills or landfill leaks.

The risk of solvent exposure was made clear in a study of 97 twin pairs where one twin has PD and the other didn’t. The exposure to trichloroethylene was found to increase the risk of PD by 6-fold, and combined exposure of perchloroethylene and carbon tetrachloride were also found to significantly increase the risk of PD. [ref]

Genetic Risk Factors for Parkinson’s Disease:

Most of these genetic variants aren’t considered to cause Parkinson’s on their own, but exposure to environmental factors along with genetic susceptibility is thought to lead to PD.

LRRK2 gene:
Mutations in this gene are linked to a higher risk of Parkinson’s disease. There are rare mutations that lead to early-onset disease. Of the LRRK2 variants listed below, the G2019S variant listed first causes the most significant increase in risk, and it may be one that you should talk to talk to your doctor about getting a second genetic test to confirm.

Check your genetic data for rs34637584 G2019S (23andMe v4, v5):

  • G/G: normal
  • A/G: significantly increased risk of Parkinson’s[ref]
  • A/A: significantly increased risk of Parkinson’s[ref]
  • Note: this genetic variant may be misreported on AncestryDNA version 2 data.

Check your genetic data for rs34778348 G2385R (23andMe v4, v5; AncestryDNA):

  • G/G: normal
  • A/G: increased risk of Parkinson’s
  • A/A: increased risk of Parkinson’s[ref][ref]

Check your genetic data for rs33995883 N2081D  ( 23andMe v4, v5; AncestryDNA):

  • A/A: normal
  • A/G: increased risk of Crohn’s disease, slight increase in risk for Parkinson’s depending on the study[ref][ref]
  • G/G: increased risk of Crohn’s disease, slight increase in risk for Parkinson’s depending on the study[ref][ref]

SNCA gene alpha-synuclein is found in the terminal of neurons.

Check your genetic data for rs2736990 (23andMe v4, v5; AncestryDNA)

  • A/A: normal risk of Parkinson’s
  • A/G: slightly increased risk of Parkinson’s (really common variant)
  • G/G: increased risk for Parkinson’s [ref]

Check your genetic data for rs356218 (AncestryDNA only):

  • A/A: normal risk of Parkinson’s
  • A/G: slight increase in risk of Parkinson’s (really common variant)
  • G/G: slight increase in the risk of Parkinson’s[ref]

PER1 gene: A circadian clock gene.

Check your genetic data for rs2253820 (23andMe v4 only; AncestryDNA):

  • T/T: normal risk of Parkinson’s
  • C/T: slight increase in risk of Parkinson’s
  • C/C: slight increased risk of Parkinson’s[ref]

SLC2A13 gene:  Facilitated glucose transport gene.

Check your genetic data for rs1994090 (23andMe v4, v5; AncestryDNA):

  • G/G: increased risk of Parkinson’s disease [ref]
  • G/T: slightly increased risk of Parkinson’s disease
  • T/T: normal

ALDH gene: Aldehyde dehydrogenase gene

Check your genetic data for rs671 ( 23andMe v4, v5; AncestryDNA):

  • G/G: normal
  • A/G: increased risk of PD with pesticide exposure, inc. dementia
  • A/A: increased risk of PD with pesticide exposure, inc. dementia[ref][ref][ref]

Goucher’s disease and Parkinson’s:

Goucher’s disease is a genetic liposomal storage disease. Most people with the disease carry two copies of a mutated GBA gene. The GBA gene codes for an enzyme called β-Glucocerebrosidase which is part of the lysosome.  People with Goucher’s disease are at an increased risk for Parkinson’s disease — and people who carry one mutation are also at an increased risk for Parkinson’s disease. A study published in the Journal of the American Medical Association found that almost 10% of the 500+ Parkinson’s patients that they investigated carried a mutation for Goucher’s disease compared with 0.3% of the control group without Parkinson’s. This leads to a 28-fold increase in the risk for Parkinson’s. [ref]

Check your genetic data for rs421016 L444P (23andMe v4):

  • A/A: normal
  • A/G: increased risk for Parkinson’s
  • G/G: increased risk for Parkinson’s and Goucher’s disease[ref][ref]

Check your genetic data for rs387906315 ( 23andMe 4000417 v4, v5):

  • DD (or –): normal
  • DI (or -C): increased risk for Parkinson’s (carrier for Goucher’s)
  • II (or C/C): increased risk for Parkinson’s and Goucher’s disease.[ref]

Check your  genetic data for rs2230288 (23andMe v4, v5):

  • C/C: normal
  • C/T: increased risk for PD
  • T/T: 2x increased risk for PD, Goucher’s[ref]

Lifehacks:

First, let me make clear that you should always talk with a doctor if you suspect you are in the early stages of Parkinson’s disease. There are many medications that can be prescribed to delay the progression of the disease.

What is listed here for lifehacks are things to look into and consider – along with whatever treatment course you’ve decided on with your doctor.

Get Your Circadian Rhythm In Sync:

This article on the circadian disruption in Parkinson’s explains that dopamine plays an important role in circadian rhythms.  Parkinson’s disease patients are likely to exhibit quite a few circadian rhythm disorder symptoms including sleep disorders, body temperature decrease, and autonomic system disruption such as blood pressure disturbance.

Another good review of circadian disruption in Parkinson’s disease. The thought is that while circadian disruption doesn’t cause Parkinson’s, the disturbance to the dopaminergic neurons possibly causes the circadian disruption, which then may exacerbate or add to the neurodegenerative process.[ref]

So if the circadian rhythm dysfunction is integral to PD, it makes sense to do everything you can to keep your circadian rhythm in sync. This would include:

  • regular sleep/wake schedule,
  • sunlight during the day to stop melatonin during the day,
  • blocking blue light at night to increase melatonin,
  • eating on a regular schedule (not too late at night).

Let me further explain the reason for blocking blue light at night:
Light in the blue wavelengths (~480nm) signals through photoreceptors in the retina that it is daytime. This blocks the production of melatonin and resets your circadian rhythm for the day. Beyond melatonin, there is a circadian rhythm to dopamine as its levels rise and fall over the course of a day. There are mouse studies showing that constant light disrupts the rhythm of dopamine production.[ref]

Photobiomodulation:

There are several studies on photobiomodulation and Parkinson’s disease. While the idea of shining infrared light on the head may seem silly at first, there is actually quite a bit of solid research on the topic.[ref][ref][ref][ref] I’m not an expert in this area, but it is something that I think is worth spending your time looking into if you are affected by Parkinson’s.

Transcranial Magnetic Stimulation:

This is another topic that I don’t know much about, but there are quite a few studies showing that ‘repetitive transcranial magnetic stimulation’ helps with the motor skills problems with Parkinson’s. A meta-analysis that combined the data from twenty-two randomized placebo-controlled studies found that the evidence showed that repetitive transcranial magnetic stimulation improved upper limb function and walking performance.[ref] Here’s more on the topic from the Mayo Clinic.

Pulsed Electromagnetic Stimulation (PEMF):

Sort of similar to the above (except more easily accessible to people) is the concept of pulsed EMF. A case study of a man with Parkinson’s who did PEMF for 30 minutes a day for 8-week sessions found that he had improved fine motor skills (better handwriting) and less muscle stiffness and fatigue.[ref]  A randomized control trial of 97 participants with PD didn’t have quite as impressive of results, although the overall outcome was positive for patients with milder PD symptoms.[ref][ref]

Other therapies:

There are a variety of other physical therapy options for PD. From exercise, physiotherapy, and aquatic therapy — to dance therapy or music therapy.[ref][ref] I encourage you to seek out options that are available in your area and appeal to you.

A diet of fresh foods:

Quite unsurprisingly, a diet that includes fresh fruit and vegetables, nuts and seeds, olive oil, fish, and fresh herbs was found to be associated with a reduced rate of PD progression. On the other side, more rapid PD progression was associated with a diet that included soda, fried foods, ice cream, cheese, and beef.  Iron supplements were also associated with more rapid PD progression. [ref]

More to read:

Michael J. Fox foundation blog

BChE – Pesticides, Parkinson’s, and Potatoes

3 Comments on “Genetic variants that increase the risk of Parkinson’s disease

  1. I have 2 female relatives with Parkinson’s disease. My sister has the early onset kind. (She began to develop symptoms sometime in her late 50s; my aunt began to develop symptoms around her mid to late 70s). We do have a lot of genes for PD and several other autoimmune diseases.
    I think that menopause plays a part in one type Parkinson’s. When estrogen runs out, it affects a woman’s sense of smell and her ability to get restorative sleep at night. (I’m over 60 and I speak from personal experience). My sister did not begin to show signs of PD until menopause. My aunt was on hormone replacement until about her mid 70s…then her doctor took her off. PD symptoms soon followed! I am on bio-identical hormone replacement; but if I run out of my RX, I notice within about 4 days that my sense of smell diminishes! Sleep also tends to suffer.

    I’m not saying that menopause causes PD. However, I think that genes, hormones, and lifestyle/ stress/ environment all play a part in developing the disease.
    It will be interesting to see what future research shows us about PD.

    • Jeane, Diminished olfaction is an early sign of Parkinson’s disease (PD), among other conditions, and your family history of PD may suggest an X (female) chromosome inheritance form of PD I am not an expert on X-linked Parkinson’s disease, but it may be highly informative for you, your aunt and sister to be evaluated genetically, though it sounds like you have already, to help you learn more about your relatives PD and your risk.

  2. I never knew that circadian disruption was involved in Parkinson’s. My uncle was a great painter, but now has Parkinson’s and is so sad he shakes. I’ll have to tell him about your tips so he has a better understanding of what is happening to him.

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