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| My brother, mother and I circa 1955 |
Heredity, genes and environmental toxins are keys to understanding what is currently known about the cause of Parkinson's Disease. In my personal quest for cause I have examined how my life history of exposure to environmental toxins fits in with the factors listed above.
The Search for Cause
It is known that a small percentage of patients acquire Parkinson’s by directly inheriting it. The inherited disease is usually seen in families of Mediterranean descent who carry specific genes that produce it. (Tanner 1) Genes are the working units of heredity and each contains DNA coded to manufacture protein for a specific purpose. Inherited genes that cause Parkinson’s are called causal genes. Causal means that If you inherit one of them you will get Parkinson’s. It will need no help from any outside source. (Gwinn 1)
In the majority of cases of PD the cause is more of a mystery and requires a bit of speculation based on information that is currently known. With this in mind it is now believed that both environmental and genetic factors play a role in causing the disease in non inherited PD. (Tanner 1) Specific gene variations have been identified as being associated with PD. These genes alone are not thought to cause the disease independently. It is believed that these “associated genes” must combine with environmental toxins and/or other genes to cause the disease. Those who have these genes may never get PD but they may. (Gwinn 1) (Tanner 1) Once the damage is done to associated genes and the process known as Parkinson’s is set in motion it cannot be stopped.
Environmentally a number of specific chemicals and occupations that put people in close contact with them have been linked to a higher risk of Parkinson’s. Possible chemical exposure and increased PD risk frequently appear in the news media and literature. Pezzoli and Cered, after an extensive review of controlled studies of PD and chemical exposure concluded that:
PD risk was increased by exposure to any-type pesticides, herbicides, and solvents. The risk associated with rural living was(also) found to be significant.
Other substances that have been identified with increased risk of PD include fungicides and the villain of Vietnam, agent orange. A drug of abuse called MPTP is known to produce Parkinson’s by itself. Recently welding has been identified as a higher risk of PD occupation
With this information in mind I reviewed periods of my life in an effort to highlight how easily exposure to chemical risk factors for PD may have occurred. Keep in mind that many of these things happened a long time ago and my memory creates an approximation at best.
Rural Living
My family moved to a small acreage when I was 5 years old. Our new home had a beautiful cherry orchard on it and the orchard was a source of both pride and supplemental income for our family. Unfortunately A major freeze in 1955 killed all of our trees. Dad was a determined man and he soon replanted the acreage with new trees and Cherries remained a part of our lives.
Organic was not thought of in the 1950's and difficult pests such as the cherry fruit fly mandated insecticidal spraying at routine intervals. My Dad paid a man to do the spraying in the early years. When I think about it I can still see the man arriving on his tractor, clothed in rain slicker clothing and towing a big tank full of spray on wheels. A noisy pump was attached to the large tank of spray and it powered a sprayer behind the tank that produced a soaking fantail of pesticide spray. The man would start the pump and then slowly drive the tractor with its fountain like sprayer up and down each row of trees, soaking everything on both sides. My mother did what she could to protect us from exposure to the spray and kept my brother and I in the house while the man did his job.
I spent endless hours in the cherry orchard in my childhood years. I recall eating ripening cherries, that still had the dried spray patterns on their skins. I had been warned about spray, but I rarely bothered even to rinse the cherries I picked from the trees. Myself and other neighborhood children played in the irrigation ditches that ran down the rows of trees as if they were clean mountain streams. We swam in the open irrigation ditches that ran through nearby farmland. The ditches without doubt carried agricultural chemical carrying runoff. I could easily say that my childhood years in rural eastern Washington were something very special. I could also say that due to my own carelessness those years were loaded with exposure to significant quantities of pesticides and other farm chemicals. I never imagined that there might be a day of reckoning much later in life.
So what about my brother who is four years older than me and is free of Parkinson’s? Why would one who grew up next to me and is an agent orange exposed Vietnam veteran remain free of the disease? The answer is likely found in the genes we inherited. Just as I am color blind and he is not, I must carry the genes that when activated went on to cause the disease and he must not carry them. Also I cannot think of any childhood friends who currently have Parkinson’s disease. This may mean that none of them possessed the genes either. Even more important, I really do not know what happened to most of them.
Hospital Pharmacy
Other periods of chemical exposure also nag at me, especially the many years of working in hospital pharmacy. In those years I worked around chemotherapeutic drugs and often reconstituted and prepared the drugs for administration. Exposure risks are very real in this environment. A group of Canadian researchers looking for contamination simply swabbed the hands of pharmacy personnel working in a chemotherapy preparation environment. Detectable amounts of contamination was found. (Astrakianakis et al 1) The protection provided for those of us who worked with chemotherapeutic drugs in 80's, 90's and even the 2000's was very inadequate by today's standards.
I have to admit that I have not been able to find a connection between long term exposure to chemotherapeutic drugs and PD but I remain suspicious. These drugs are highly toxic and both acute and chronic health risks have been attributed to them. (The National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention (CDC)1)
I have thought of many additional exposures to chemical toxins in my life. These span the home ownership years and range from diazinon to Penta, a now banned wood preservative.
I am left to wonder how the things we are learning about "causal genes, associated genes"and environmental toxins could be of value to others. Therapeutic intervention in the roles inherited "causal" genes play in the genesis of PD will require further research. The influence of the array of chemicals that have become environmental toxins have on "associated" genes can be modified at least in part by our own choices and actions. More importantly we can have a part in warning the generations yet to come that poisoning our environment with environmental hazards is not without consequences. And most urgently: Teach your children well.
Shakey in Coupeville
Sources
- What Causes Parkinson Disease?Medscape interviews Caroline Tanner, MD, PhD, on major advances in the understanding of Parkinson disease, along with potential therapeutic approaches. Medscape Neurology, July 2012
- Genetics and Parkinson's Disease: What Have We Learned? By Katrina Gwinn, M.D. Originally published in the winter 2009 issue of PDF's Newsletter, News & Review.
- Exposure to pesticides or solvents and risk of Parkinson disease. Pezzoli G, Cereda E.Neurology. 2013 May 28;80(22):2035-41. doi: 10.1212/WNL. [PubMed - indexed for MEDLINE]
- Can J Hosp Pharm. 2011 Sep-Oct; 64(5): 327–332. Pilot Evaluation of Dermal Contamination by Antineoplastic Drugs among Hospital Pharmacy Personnel. George Astrakianakis, PhD, Quinn Danyluk, MSc, CIH, Winnie Chu, Chun-Yip Hon, MSc(A), CIH, CRSP, is a PhD candidate in the School of Population and Public Health, The University of British Columbia, Vancouver, British Columbia. At the time this study was performed, he was also with Disability Management and Safety, Vancouver Coastal Health, Vancouver, British Columbia
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