What is Parkinson's disease (PD)? A progressive nervous disease occurring most often after the age of 50, associated with the destruction of brain cells that produce dopamine,and characterized by muscular tremor, slowing of movement,partial facial paralysis,peculiarity of gait(步态)t and posture,and weakness.What is Parkinson’s disease (PD)? A progressive nervous disease occurring most often after the age of 50, associated with the destruction of brain cells that produce dopamine, and characterized by muscular tremor, slowing of movement, partial facial paralysis, peculiarity of gait （步态 ） and posture, and weakness