Young Onset Parkinson’s Disease is defined by age of onset less than 40 years of age.  (Some authors use a looser definition of 50 years of age.)  Up to 10% of people with PD may be classified.  A higher percentage of young-onset patients have a genetic form of PD compared older or typical age of onset patients. Younger patients may have a higher tendency to develop motor complications such as wearing off and dyskinesias with levodopa therapy compared to older patients.