G20: Parkinson disease

Parkinson's disease is a progressive nervous system disorder that primarily affects movement, especially motor function. It develops gradually, sometimes starting off with a barely noticeable tremor in one hand. While a tremor may be the most well-known sign of Parkinson's disease, the disorder can also cause stiffness or slowing of movement. As the disease progresses, these symptoms become more pronounced and may be accompanied by other symptoms such as impaired posture and balance, loss of automatic movements like blinking, and speech and writing changes. Parkinson's disease symptoms result from a decline in cells in a small part of the brain called the substantia nigra that produce dopamine, a chemical that sends signals to coordinate movement. The cause of this decline isn't well understood, but several genetic and environmental factors appear to play a role.