Parkinson's Disease

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Overview

Parkinson's disease is a chronic, progressive neurodegenerative movement disorder. Tremors, rigidity, slow movement (bradykinesia), poor balance, and difficulty walking (called parkinsonian gait) are characteristic primary symptoms of Parkinson's disease.

Idiopathic Parkinson's disease is the most common form of parkinsonism, a group of movement disorders that have similar features and symptoms. Parkinson's disease is called idiopathic Parkinson's because the cause is unknown. In the other forms of parkinsonism, a cause is known or suspected.

Parkinson's results from the degeneration of dopamine-producing nerve cells in the brain, specifically in the substantia nigra and the locus coeruleus. Dopamine is a neurotransmitter that stimulates motor neurons, those nerve cells that control the muscles. When dopamine production is depleted, the motor system nerves are unable to control movement and coordination. Parkinson's disease patients have lost 80% or more of their dopamine-producing cells by the time symptoms appear.

Incidence and Prevalence
Parkinson's disease afflicts 1 to 1 1/2 million people in the United States. The disorder occurs in all races but is somewhat more prevalent among Caucasians. Men are affected slightly more often than women.

Symptoms of Parkinson's disease may appear at any age, but the average age of onset is 60. It is rare in people younger than 30 and risk increases with age. It is estimated that 5% to 10% of patients experience symptoms before the age of 40.

Risk Factors

In a small number of cases worldwide there is a strong inheritance pattern. A genetic predisposition for Parkinson's disease is possible, with the onset of disease and its gradual development dependant on a trigger, such as trauma, other illness, or exposure to an environmental toxin.

The risk increases with age, as Parkinson's disease generally manifests in the middle or late years of life.

Causes

The cause of Parkinson's disease is unknown. Many researchers believe that several factors combined are involved: free radicals, accelerated aging, environmental toxins, and genetic predisposition.

It may be that free radicals—unstable and potentially damaging molecules that lack on electron—are involved in the degeneration of dopamine-producing cells. Free radicals add an electron by reacting with nearby molecules in a process called oxidation, which can damage nerve cells. Chemicals called antioxidants normally protect cells from oxidative stress and damage. If antioxidative action fails to protect dopamine-producing nerve cells, they could be damaged and, subsequently, Parkinson's disease could develop.

Dysfunctional antioxidative mechanisms are associated with older age as well, suggesting that the acceleration of age-related changes in dopamine production may be a factor.

Exposure to an environmental toxin, such as a pesticide, that inhibits dopamine production and produces free radicals and oxidation damage may be involved.

Roughly one-fifth of Parkinson's disease patients have at least one relative with parkinsonian symptoms, suggesting that a genetic factor may be involved. Several genes that cause symptoms in younger patients have been identified. Most researchers believe, however, that most cases are not caused by genetic factors alone.

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