Research of Parkinson's disease has shown that there are multiple causes for this progressive neurological disorder. There is a genetic component, it is age related, and there are documented cases of drug induced Parkinsonism. There are also several theories being studied which could be additional causes.
In 1817, Dr. James Parkinson of London published his “Essay on the Shaking Palsy.” The condition came to be known as Parkinson’s disease. Although much research has been conducted over the years to study this progressive neuro-degenerative disorder, medical science has yet to develop a definitive lab test to diagnose PD in a living patient. After death, an autopsy will show a reduction in the dopamine-producing neurons in a part of the brain called the substantia nigra.
In a living patient, the diagnosis is made by observing the symptoms: resting tremor, muscle stiffness (rigidity), slowness or poverty of movement (bradykinesia), postural instability, as well as a positive response to medication (Levodopa).
Most physicians are not qualified to make this diagnosis. A referral to a neurologist specializing in movement disorders is usually needed. There are many different presentations of Parkinson’s disease, and there are many conditions that are knows as Parkinsonism syndromes, which have similar symptoms but do not respond to treatment with Levodopa.
Parkinson’s disease research suggests that there are multiple causes for the death of dopamine-producing neurons. There are also a few theories that are being studied.
Genetic researchers have found mutations on about ten genes that may contribute to a hereditary form of the disease, but this accounts for less than ten percent of people with PD.
There have been documented cases where illicit drug users have unintentionally produced the toxin MPTP when they were attempting to make MPPP, a synthetic opioid drug that gives a high like heroin. Injected MPTP can cross the blood/brain barrier and destroy dopamine-producing neurons. This results in the sudden onset of permanent Parkinsonism.
The normal aging process also causes the degeneration of brain cells. The incidence of PD in the population aged 40 – 60 is 1/1000. After age 70, the incidence of Parkinson’s climbs to 1/100.
Medical scientists are working on several theories about the causes of Parkinson’s disease. If they can figure out what is killing the neurons, perhaps the damage could be prevented, or even reversed.
Researchers have pretty much ruled out diet, exercise, and stress as causes of PD, although they definitely play a part in coping with the disease.
The most common theory today is that Parkinson’s is caused by a combination of factors. Genetics makes some people more susceptible to the disease. Environmental toxins such as pesticides likely play a part. Other suspects include viruses and the bacteria in well water. It is also widely suspected that there are many more people living with undiagnosed PD.
Geography is a factor in the prevalence of PD. Actor Michael J. Fox is one of five members of a cast and crew of about forty who developed Parkinson's disease after working together on the television series Leo and Me in Vancouver, British Columbia in Canada. This could be coincidence, but it is possible that there was an enivironmental factor that contributed to this high incidence.
Statistics show that there are some places where the incidence of PD is much higher than average.
The highest incidence of Parkinson’s disease is found in the Amish communities of the northeastern states of the United States. This people group has an incredible 970 PD cases per 100,000 people. This is two to three times higher than anywhere else in the world. At first it was theorized that they had a stronger genetic component than the general population because of inbreeding in a closed community, but research has suggested that this is not the case. The cause of this anomaly is still unknown. It could be that their largely agrarian lifestyle has exposed the community to higher than normal pesticide levels.
The lowest incidence is in Ethiopia, with only 7 per 100,000 people. This may be the result of the tragically short life expectancy of the Ethiopian people. Parkinson’s is more common in the elderly. It could also be that there are many undiagnosed cases of PD.
My source for much of this information, including the statistic involving Michael J. Fox is my own collection of notes from various conferences and seminars.