What is Parkinson's Disease?

Understanding the Basics of PD

So what exactly is Parkinson's disease (PD)? PD is a type of movement disorder that can affect the ability to perform common, daily activities. Although PD is associated with a wide range of symptoms, there are features of PD that most people with the condition will experience. These symptoms are typically divided into those that affect movement (motor symptoms) and those that do not (non-motor symptoms).

The most common motor symptoms of PD are tremor (a form of rhythmic shaking), stiffness or rigidity of the muscles, and slowness of movement (called bradykinesia). A person with PD may also have trouble with posture, balance, coordination, and walking. Common non-motor symptoms of PD include sleep problems, constipation, anxiety, depression, and fatigue, among others.

It is important to note that, although there are common symptoms of PD, they can vary greatly from person to person. Moreover, how these symptoms change over time and whether other symptoms of PD emerge differ from person to person. Most people who develop the symptoms of PD do so sometime after the age of 50, but PD can affect younger persons as well. There are an estimated 1 million Americans living with PD and more than 10 million people worldwide.

How Parkinson's Disease Affects the Brain

What makes PD distinctive from other movement disorders is that cell loss occurs in a very specific region of the brain called the substantia nigra (sub-STAN-she-uh NYE-gruh). The nerve cells, or neurons, in this region actually appear dark under a microscope (substantia nigra is Latin for "black substance").

Those dark neurons produce a specific type of neurotransmitter (a chemical messenger that allows neurons to communicate) called dopamine. The neurotransmitter dopamine helps to regulate movement. This loss of dopamine is the reason that many treatments for PD are intended to increase dopamine levels in the brain.

In addition to decreases in dopamine and the cells that make dopamine, you might also read or hear about alpha-synuclein (AL-fa-sin-NUKE-lee-un). We do not yet know what this protein does in the healthy brain, but in PD it clumps up in what are called Lewy (LOO-ee) bodies. Researchers believe that alphasynuclein build-up contributes to the cause of PD and that it may be possible to develop new treatments based on this idea.

Future research will hopefully tell us more about this protein.

Theories About What Causes Parkinson's

The cause of PD is still unknown, although there is some evidence for the role of genetics, environmental factors, or a combination of both. It is also possible that there may be more than one cause of PD. Scientists generally believe that both genetics and environment interact to cause PD in most people who have it.

Currently, there is an enormous amount of research directed at producing more answers about what causes PD and how it might be prevented or cured. When physicians diagnose PD, they often describe it as idiopathic (ID-ee-oh-PATH-ik). This simply means that the cause of PD is not known.

Genetic Factors

Scientists estimate that less than 10% of cases of PD are primarily due to genetic causes. The most common genetic effect that triggers PD is mutation in a gene called LRRK2. The LRRK2 defect is particularly frequent in families of North African or Jewish descent. Mutations in alpha-synuclein have also been found to trigger PD, but these are quite rare. In most cases of PD, no primary genetic cause can be found.

Environmental Factors

Certain environmental factors, such as significant exposure to pesticides or certain heavy metals and repeated head injuries, can increase risk of PD. Most people do not have a clear environmental cause for their PD, and because many years can pass between exposure to an environmental factor and the appearance of PD symptoms, the connection is often difficult to establish. However, it seems likely that environmental factors do influence the development of PD, perhaps particularly in people who also have a genetic susceptibility.

Other Risk Factors

There are other things that put an individual at higher risk for developing PD. The main risk factor is age, because PD is more common in older adults (>50 years of age). Men also have a higher risk of PD than women. PD often seems to affect Caucasians more than African Americans or Asians. The actual links between any of these factors and PD are not completely understood.

Further Reading:

Symptoms of PD
Treatment & Medications
Living with Parkinson's
Parkinson's Disease Handbook

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