Parkinson disease (PD) is common in the general population,
and as more and more people live into their eighties, the
clinical, economic and emotional impact of this neurodegenerative
disease will dramatically increase in magnitude. Although
current therapies can alleviate some symptoms in the short
term, the disease never remits and symptoms grow worse over
time. PD may ultimately be disabling, but since the disease
often progresses gradually, most people lead productive lives
for many years after diagnosis.
PD generally affects people over the age of 50 years, with
only 15% of those affected showing symptoms before the age
of 50. It is estimated that more than 1% of 55 year-old individuals
are affected and more than 3% of those over 75 years-of-age
have the disease. It appears to be more common among men then
women; however, this is not known for sure. Current treatment
of PD relies on symptom alleviation through drug treatment
or surgical intervention. How well an individual responds
to drug treatment is also useful in confirming the diagnosis
of Parkinson’s disease.
Scientists have been able to identify why people get Parkinson
disease – cells in a certain part of the brain, called
the substantia nigra, die off. Under normal circumstances,
these neuronal cells produce an important brain chemical known
as dopamine. When these cells die or are otherwise unable
to produce dopamine, symptoms of Parkinson disease begin to
appear. Common symptoms include slowness of movement and reflexes
(bradykinesia), rigidity in the arms and legs, tremors and
difficulty with balancing and walking.
Although we know which cells die off, the precise reason
why they die is not always clear. A few families have a mutation
in one of the disease causing genes, which would account for
why certain families have many affected individuals. A mutation
in a single gene is rare cause of PD, however. Other individuals
can trace the cause of their disease back to exposure to a
specific toxin, but these too are relatively rare. Most cases
of PD are idiopathic (i.e. of unknown cause), and are probably
due to a complex interaction between environmental factors
and susceptibility genes. Learn
about the Genetics of PD.
Another cause of Parkinson disease can be acute head trauma.
In fact, head trauma is the strongest predictor of PD in several
epidemiological studies. This must be put into perspective,
however. A common estimate of the number of traumatic brain
injuries in the United States is 1.5 million per year, and
yet most of these individuals do not develop PD. Furthermore,
most individuals with PD have not had a traumatic brain injury.
The fact that a head injury is the biggest predictor of PD
shows first and foremost, that we do not yet know why most
people develop the disease.
A cure has not yet been discovered for Parkinson disease;
however, there are a number of effective treatments for the
disease. Most of the symptoms associated with PD are due to
a lack of dopamine in the brain. Therefore, most of the medications
currently used to treat PD either increase dopamine levels
or use similar compounds to mimic the effects of dopamine.
These types of drugs are often able to alleviate the tremor
but not the other symptoms. Some patients consider their tremor
to be the most distressing symptom because of its visibility
to others, but this symptom rarely leads to serious disability
and approximately a quarter of PD patients do not even have
this symptom. Bradykinesia and stiffness are often more worrisome
as they can lead to falls and subsequent injuries. It should
be emphasized that symptoms will vary from patient to patient
with both the type and severity of symptoms.
Since PD results from such a complex mixture of genetic and
environmental causes, many studies, such as this one, are
focused on identifying susceptibility genes and environmental
risk factors. During the next several decades, hopefully this
research will yield the knowledge necessary to treat and,
ideally, prevent the disease.
For more information, see:
The Genetics of Parkinson's
Some basics on genetics and how genetics affect the development
of Parkinson's Disease.
Other sites with information on Parkinson's Disease.