Parkinson’s disease is a nervous system disease that affects movement. It develops gradually, sometimes starting with a tremor that is barely noticeable on one hand. It also causes stiffness and slow movement.
Parkinson’s disease is a degenerative disease resulting from the slow, progressive death of neurons in the brain. Because the part of the brain affected by the disease plays an important role in controlling our movements, people with Parkinson’s disease gradually make stiff and uncontrollable movements. For example, it becomes difficult to bring a cup to the lips with precision and smoothness. Today, available treatments can reduce symptoms quite effectively and slow the progression of the disease. A person can live with Parkinson’s disease for many years.
Parkinson’s disease usually occurs between the ages of 50 and 70. The average age of onset of the disease in the US is 60. At first, the symptoms may be mistaken for normal aging, but as they get worse, the diagnosis becomes clearer.
When the first symptoms appear, an estimated 60% to 80% of dark matter nerve cells have already been destroyed. Thus, when symptoms appear, the disease has already progressed by an average of 5 to 10 years.
Worldwide, more than 300,000 people are diagnosed with the disease each year. The number of cases increases with age. An estimated 1 in 100 people are affected at age 65, and 2 in 100 people at age 70 and older. At the heart of the disease: a dopamine imbalance.
Nerve cells affected by Parkinson’s disease are located in an area called “dark matter” in the center of the brain. The cells in this area produce dopamine, a chemical messenger ( a neurotransmitter) that helps control movement but also acts on feelings of pleasure and desire. The death of the dark matter cells causes a shortage of dopamine, which leads to an increase in acetylcholine and glutamate (two other chemical messengers). This imbalance causes the occurrence of the disease symptoms, namely tremors, muscle stiffness, and the inability to perform certain movements. On the other hand, an excess of dopamine can cause symptoms associated with schizophrenia.
What causes the progressive loss of neurons in Parkinson’s disease remains unknown in most cases. Scientists agree that a combination of genetic and environmental factors plays a role, although these cannot always be clearly defined. The current consensus is that the environment plays a more important role than heredity, but that genetic factors would prevail when the disease occurs before age 50. Here are some of the environmental factors involved:
- Early or prolonged exposure to chemical pollutants or pesticides, including herbicides and insecticides (e.g., rotenone).
- MPTP, a drug that sometimes contaminates heroin, can suddenly cause a severe and irreversible form of Parkinson’s disease. This drug acts in the same way as rotenone pesticide.
- Carbon monoxide or manganese poisoning.
Researchers have also found that many changes occur in the brains of people with Parkinson’s disease, although the reasons for these changes have not been determined. These changes include:
- The presence of Lewy bodies, which are substances present in brain cells (neurons). Researchers believe that these Lewy bodies play a toxic role in Parkinson’s disease.
- The presence of alpha-synuclein in Lewy bodies. Although there are many substances present in Lewy’s bodies, scientists believe that alpha-synuclein is a protein that plays a harmful role when it is in an aggregated form that cannot be resolved by cells.