Parkinson disease (PD) is the second most common neurodegenerative disease after Alzheimer disease. It has an age-adjusted prevalence of approximately 150 of 100 000 and 2% at age 75 years. The early clinical features predominantly involve motor deficits that include asymmetric onset of resting tremor (usually upper limb), bradykinesia, and rigidity. These are, for the most part, the consequence of loss of dopaminergic neurons in the substantia nigra pars compacta. An important morphological hallmark of PD is the presence of Lewy bodies in a proportion of surviving neurons.
Schapira AHV. The Importance of LRRK2 Mutations in Parkinson Disease. Arch Neurol. 2006;63(9):1225-1228. doi:10.1001/archneur.63.9.1225