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I have read an article about Parkinson's disease in VOA news site. My father had ever suffered from this disease.
The essentials are as follows.

Parkinson's is a disease of the central nervous system. It is a progressive disorder. The disease affects a small area of cells in the middle of the brain. The cells slowly lose their ability to produce a chemical substance called dopamine.

I just have a pain in my nervous system, so the rest is omitted.