Parkinson disease (PD) is a neurodegenerative disease usually typified by slow onset in mid to late adulthood; there are also early-onset and juvenile forms of the disease. Symptoms worsen over time and include resting tremor, muscular rigidity, bradykinesia [abnormal slowness of movement], and postural instability [impaired balance and coordination]; additional symptoms may include postural abnormalities, dysautonomia [symptoms caused by malfunction of the autonomic nervous system], dystonic cramps, and dementia. Parkinson disease is the second-most common neurodegenerative disease (after Alzheimer disease), affecting approximately 1% of the population over 50 (Polymeropoulos et al., 1996, pubmed:8895469). [from MIM:168600; 2013.07.23]

Parkinson disease is described as early-onset disease if signs and symptoms begin before age 50. Early-onset cases that begin before age 20 may be referred to as juvenile-onset disease. [from Genetics Home Reference, GHR_condition:parkinson-disease, 2015.02.13]