Who Gets Parkinson's Disease?
About 50,000 Americans are diagnosed with PD 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 PD and there is no
definitive test for the disease. People with PD may sometimes be
told by their doctors that they have other disorders, and people
with PD-like diseases may be incorrectly diagnosed as having PD.
PD strikes about 50 percent 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 PD is age. The average age of onset is 60
years, and the incidence rises significantly with increasing age.
However, about 5 to 10 percent of people with PD 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 PD have an increased risk of developing the
disease themselves, but the total risk is still just 2 to 5 percent
unless the family has a known gene mutation for the disease. An
estimated 15 to 25 percent of people with PD 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.
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