Parkinson's disease is a degenerative disorder of the central nervous system that affects between one-and-a-half million and two million Americans. The incidence of PD is often underestimated because it is not contagious and does not have to be reported by physicians. PD may appear at any age, but it is uncommon in people younger than 40, and the risk of developing it increases with age. It occurs in all parts of the world, and men are affected slightly more often than women.

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