nearly 50 000 americans are diagnosed with parkinson's disease each year but getting an accurate count of the number of cases may be impossible because many people in the early stages of the disease assume their symptoms are the result of normal aging and do not seek help from a physician. also diagnosis is sometimes difficult and uncertain because other conditions may produce symptoms of parkinson's disease and there is no definitive test for the disease. people with parkinson's disease may sometimes be told by their doctors that they have other disorders and people with parkinson's disease-like diseases may be incorrectly diagnosed as having parkinson's disease. parkinson's disease strikes about 50% more men than women but the reasons for this discrepancy are unclear. while it occurs in people throughout the world a number of studies have found a higher incidence in developed countries possibly because of increased exposure to pesticides or other toxins in those countries. other studies have found an increased risk in people who live in rural areas and in those who work in certain professions although the studies to date are not conclusive and the reasons for the apparent risks are not clear. one clear risk factor for parkinson's disease is age. the average age of onset is 60 years and the incidence rises significantly with increasing age. however about 5% to 10% of people with parkinson's disease have "early onset" disease that begins before the age of 50. early onset forms of the disease are often inherited though not always and some have been linked to specific gene mutations. people with one or more close relatives who have parkinson's disease have an increased risk of developing the disease themselves but the total risk is still just 2%-5% unless the family has a known gene mutation for the disease. an estimated 15%-25% of people with parkinson's disease have a known relative with the disease. in very rare cases parkinsonian symptoms may appear in people before the age of 20. this condition is called juvenile parkinsonism. it is most commonly seen in japan but has been found in other countries as well. it usually begins with dystonia and bradykinesia and the symptoms often improve with levodopa medication. juvenile parkinsonism often runs in families and is sometimes linked to a mutated parkin gene.
who gets parkinson's disease?