Parkinson’s Disease

 What we know
 Incidence
 Costs
 Environmental risk factors

What we know

Parkinson’s disease (PD) is a degenerative neurological disease characterised by motor skill and speech impairments. Symptoms include rigidity, instability, and tremor. The disease occurs as a result of a loss of nerve cells that produce dopamine in the substancia negra part of the brain that coordinates movement. Parkinson’s symptoms begin to appear when about 80% of the dopamine has been lost. Most people are diagnosed between the ages on 40 and 60, although a small minority is diagnosed between the ages of 30 and 40.

Incidence

Parkinson’s disease affects people of all races, socioeconomic levels and geographic regions. After Alzheimer’s disease it is the second most common neurodegenerative disease. In Europe the incidence ratio is approximately 20 new cases per 100,000 people per year.[Leslie Findley, Manjit Aujila, Peter G. Brain, Mary Baker, Catherine Beech, Clive Bowman Jeremy Holmes, Wendy K. Kingdom Douglas G. MacMahon, Vib Peto and Jeremy R. Playfer (2003) [1], [2]. Unlike with other chronic diseases little is known about trends in incidence and prevalence of PD or Parkinsonism over time, or geographic variation in rates.

Figure 1. Total number of cases of disorders of the brain in Europe by specific disorder (million) [3]

Costs

The literature reviewed reports significant health care costs for patients with PD, ranging from € 5000 to € 10,000 per patient and year and in total Parkinson’s disease is thought to cost European Society Euros 11 billion [4].

Figure 2. Cost per case of in specific brain disorders in Europe (€PPP 2004). [5]

Environmental risk factors

There is evidence that both genetic and environmental factors are important determinants. Although the data are inconclusive, chronic , low-dose exposure to pesticides is suspected to increase the risk for Parkinson’s disease. Several studies implicate the pesticides rotenone, paraquat, some fungicides such as maneb, and organochlorine pesticides like dieldrin [6], [7] :

 Rotenone is a plant-based pesticide that is often used to kill fish that are considered undesirable or a threat to recreational of commercial fisheries
 Paraquat is a compound similar to MPTP, which in the 1980s was mistakenly used by some San Francisco drug users resulting in them developing irreversible Parkinson’s like symptoms. Paraquat is frequently used on corn, soybeans, cotton and fruit.
 Fungicides such as Maneb contain the heavy metal manganese, associated with Parkinson-like symptoms. Amongst other things, Maneb is used on corn, potatoes, lettuce and tomatoes.
 Dieldrin is a pesticide whose neurotoxin dopamine-depleting effects have been observed in ducks, doves and rats.

The latest study from the EU-funded GeoParkinson, argues that the risk of developing Parkinson’s disease increases according to the level of pesticide exposure [8]. The study, which investigated the relationship between exposure to solvents, pesticides, iron, copper and manganese and the risk of PD, is one of the largest case-control studies to date of genetic, environmental, and occupational risk factors for Parkinson’s disease or other degenerative Parkinsonian syndromes.

Various explanations have been put forward regarding the mechanism by which chemicals might be affecting nerve cells of the substancia negra. One hypothesis is that low levels of chemicals over time may instigate a molecular chain of events in the brain that eventually leads to Parkinson’s. Alternatively, certain substances may lead to inflammation of the brain, which in turn reduces the body’s resistance to toxins. It has also been suggested that chemicals affect, alter gene expression, and thereby affect cell processes involved in cell death. [9].

It is postulated that early life exposures to environmental toxins may determine the development of PD [10]. Furthermore, people are not equally predisposed to toxic insults, and it is probable that susceptibility is determined genetically. Scientific speculation is that a cluster of genes, acting in concert, define an individual’s vulnerability to environmental agents.

In addition to pesticides other risk factors for Parkinson’s include: having had a head injury, having a history of depression, viral infection, being frequently exposed to solvents, and rural living and well water.

Overall, there is strong evidence that PD is caused in part by environmental exposure. Pesticides may be an important causative and potentially modifiable risk factor. This has implications for occupational and, perhaps, recreational users of these agents. Whilst further research is needed to establish causative mechanisms and which environmental factors are associated with PD, the fact that the incidence of PD is bound to increase with advancing age and that many Western societies face an aging population creates a powerful imperative to better understand the means of preventing PD and institute precautionary measures to avoid potential risk factors.

 For more information see the Collaborative on Health and Environment Parkinson’s Disease Working Group