Are You at Risk tor Parkinson's Disease?

Excerpted from
What Your Doctor May Not Tell You About Parkinson's Disease: A Holistic Program for Optimal Wellness
By Jill Marjama-Lyons, M.D., Mary J. Shomon

Although the cause of Parkinson's disease is unknown, a number of environmental, toxic, and genetic factors have been linked to the condition. Other factors such as hormone levels and the use of caffeine and nicotine have been proposed as playing a role in the development of Parkinson's disease as well. Ultimately, however, not one single environmental agent has been proven to directly cause Parkinson's disease. And because there has never been an epidemic outbreak of Parkinson's disease, it is unlikely that a single environmental cause exists. Even though several genes have been identified as causes, a purely genetic cause for Parkinson's disease appears to apply to only a very small number of people. The reality is that environmental or toxic exposures, nutritional deficiencies, stressors, and physical and genetic susceptibility combine to trigger Parkinson's disease.

Nature Versus Nurture?

Scientists in the late 1800s described Parkinson's disease as a purely genetic disorder, and the debate still goes on today regarding whether Parkinson's disease is a genetic (nature) or environmentally derived (nurture) illness. Parkinson's disease was viewed as an inherited disease for some time, until the outbreak of viral encephalitis lethargica-known as sleeping sickness-during World War I. Encephalitis lethargica was described as a slowly progressive parkinsonian syndrome similar to Parkinson's disease.

After this, scientists looked for other possible environmental causes of Parkinson's disease, such as viruses and exposure to heavy metals or toxic chemicals in the workplace. A higher incidence and prevalence of Parkinson's disease was observed with exposure to some of these chemicals and gave credence to the environmental theory. This was even further supported by the discovery that MPTP (a chemically designed synthetic heroin for intravenous drug abusers) induced Parkinson's syndrome in young Northern California IV drug users in the 1980s. However, the compound-MPTP, and its toxic metabolite, MPP+-is not found, except as a designer street drug, in other common chemical sources and cannot account for the large number of persons that develop Parkinson's disease.

In the early 1990s, Dr. Lawrence Golbe described a familial form of Parkinson's disease that affected many members of one very large family of Greek-Italian descent. The gene that caused the disease in this family was then discovered, and the search by geneticists for other genes linked to Parkinson's disease was then reawakened. Several different genes have since been found as causes of the condition, and so the pendulum has begun to swing back toward the genetic theory of Parkinson's disease once again.

Risk Factor: Gender

Parkinson's disease affects both men and women, but the majority of studies have found Parkinson's disease to be slightly more common in men than in women. This trend persists globally, especially in China, where men are three times more likely to get Parkinson's disease than women. Another study found that African, Hispanic, and Caucasian women had a lower incidence of Parkinson's disease than men of the same ethnic groups. One study reported a twofold increase in Parkinson's disease among Italian men across all ages. The explanation for this increased risk in men is not known. It may represent a hormonal effect-estrogen, the primary female hormone, may protect dopamine brain cells from dying. It could also be an environmental/occupational effect, as men are more likely to pursue occupations that expose them to the toxins that are causally linked to Parkinson's disease.

Risk Factor: Age

An increase in age is associated with an increased risk of Parkinson's disease. This has been observed across all cultures and in both sexes. The incidence of Parkinson's disease in one year is less than 10 per 100,000 for persons under the age of 50, compared to over 200 per 100,000 by age 80. It has been estimated that 5 to 10 percent of patients with Parkinson's disease experience the onset of their symptoms before age 40, and the peak incidence of onset of Parkinson's disease is between 55 and 60. Interestingly, the number of persons diagnosed with Parkinson's disease lessens after age 80, suggesting that the condition is not simply a process due to aging of the brain.

While Parkinson's disease is not necessarily a disease of the elderly, it appears to be on the rise, because as a progressive illness, the risk grows with increased age. So, as the population ages, the number of persons with Parkinson's disease increases.

Risk Factor: Ethnicity

The prevalence of Parkinson's disease appears to vary among races somewhat, and it's thought that there is a higher prevalence in countries where the majority of the population is Caucasian (100 to 300 cases of Parkinson's disease per 100,000 in North America and Europe). The conventional wisdom has also claimed a lower prevalence in Asian and African countries, with 50 eases of Parkinson's disease per 100,000. However, many of these studies are now coming to light as being flawed, and more recent studies have shown a higher prevalence of Parkinson's disease in Americans of African and Asian descent, similar to levels seen in Caucasian Americans. While the prevalence and incidence of Parkinson's disease in Native Americans has not been formally studied, some experts suggest that the prevalence is greater than we originally-thought, and may be equal to or even higher than other groups in the American population.

Risk Factor: Geographic Region

The estimated prevalence of Parkinson's disease does vary from region to region. What this means, however, is debatable. For example, 31 per 100,000 persons living in Libya have Parkinson's disease, while the rate is 328 per 100,000 in Bombay, India. Several studies have shown a difference in the incidence and prevalence of Parkinson's disease in various regions of the United States. These differences could be due to less access to health care, genetic differences in susceptibility to disease, or differences in exposure to causative environmental agents. Even migration patterns can factor into the analysis. If one looks at the state of Florida, for example, with a total population of 16 million, using the standard calculations, 17,600 persons should have Parkinson's disease. However, because Florida is a retirement state, 3.5 million persons are over the age of 60 and the prevalence is therefore even higher, with nearly 40,000 Floridians estimated to have Parkinson's disease.

A higher incidence of Parkinson's disease has been found in persons who live in a rural setting in comparison to those who live in the city. Dr. Jean Hubble showed a higher occurrence of Parkinson's disease in residents of rural western Kansas compared to those who lived in the city, and other similar studies have confirmed this observation.