Parkinson’s disease (also known as Parkinson disease, Parkinson’s, idiopathic parkinsonism, primary parkinsonism, PD, hypokinetic rigid syndrome/HRS, or paralysis agitans) is a degenerative disorder of the central nervous system. The motor symptoms of Parkinson’s disease result from the death of dopamine-generating cells in the substantia nigra, a region of the midbrain; the cause of this cell death is unknown.