Parkinson's disease is caused by the progressive impairment or deterioration of neurons (nerve cells) in an area of the brain known as the substantia nigra. When functioning normally, these neurons produce a vital brain chemical known as dopamine. Dopamine serves as a chemical messenger allowing communication between the substantia nigra and another area of the brain called the corpus striatum. This communication coordinates smooth and balanced muscle movement. A lack of dopamine results in abnormal nerve functioning, causing a loss in the ability to control body movements.
Why Does Parkinson's Disease Occur?
Why Parkinson's disease occurs and how the neurons become impaired is not known. However, there is increasing evidence that Parkinson's disease may be inherited (passed on genetically from family members).
There is considerable controversy surrounding the possibility of a genetic cause of Parkinson's disease. In a small number of families, specific genetic abnormalities leading to the illness have been identified. However, the vast majority of people with Parkinson's disease do not have one of these identified genetic abnormalities. It is probable that in people who develop Parkinson's disease early in life (called young-onset Parkinson's disease) there is a genetic component. Because we don't understand very much at this point about how Parkinson's disease is inherited, the implications for children of people with Parkinson's disease are unclear.
There is also some evidence that certain toxins in the environment may cause Parkinson's disease. Scientists have suggested that external or internal toxins may selectively destroy the dopaminergic neurons, causing Parkinson's disease. Toxins that may be linked to Parkinson's include manganese, carbon monoxide, carbon disulfide, and some other pesticides.
Also, it is believed that oxidative stress can cause Parkinson's disease. Oxidation is a process in which free radicals (unstable molecules lacking one electron), in an attempt to replace the missing electron, react with other molecules (such as iron). Free radicals are normally formed in the brain and body, but usually the brain and body have mechanisms to get rid of them. In people with Parkinson's disease, the mechanisms may not be effective or they may produce too many free radicals. It is also possible that environmental toxins may contribute to abnormal free radical formation and lead to Parkinson's disease. Oxidation is thought to cause damage to tissues, including neurons. In most cases, antioxidants protect cells from free radical damage.
While it is not clear what events cause the abnormal nerve function linked to Parkinson's disease, there are certain conditions and medications that can cause Parkinson's disease-like symptoms. These include:
- Certain medications. Certain drugs such as antipsychotics used to treat severe paranoia and schizophrenia can cause a person to experience symptoms that resemble Parkinson's disease (Parkinsonism).
- Shy-Drager syndrome. This is a rare degenerative condition that produces symptoms similar to Parkinson's disease.
- Street drugs. MPTP, a synthetic heroin contaminant, can cause severe Parkinson's disease-like symptoms.
- Blood vessel disorders. Although rare, stroke and atherosclerosis (hardening of the arteries) can cause symptoms similar to Parkinson's disease.
Most researchers suggest that a combination of these factors may cause the disease.
Can Parkinson's Disease Be Prevented?
To date, there is no known prevention or cure for Parkinson's disease. But, there are several treatment options, including drug therapy and/or surgery that can reduce the symptoms, and make living with the disease easier.