Parkinson's Disease

NIEHS is one of the lead research agencies studying environmental links to Parkinson\u2019s disease. The institute works closely with other research programs within the National Institutes of Health (NIH), as well as partners and scientists across the country, to look at every aspect of this disease.

What Is Parkinson's Disease?

Parkinson's disease is neurodegenerative, the second most common disorder of this type after Alzheimer's disease.

Within your body, nerves transmit information to and from the brain or spinal cord, which affects muscles and organs. Neurodegeneration means that your nerves are not functioning normally. Parkinson\u2019s disease is a progressive and unending movement disorder.

How Many People Are Affected by Parkinson's Disease?

It is difficult to know exactly how many people have Parkinson's disease because there is no national registry. But it is estimated that nearly 1 million people in the U.S. have the disease. The average age of onset is about 60. A study estimated that population prevalence increases from about 1% at age 60 to 4% by age 80.

Parkinson's strikes people of all races, ethnic groups, nationalities, and income levels. Well-known people with the disease include actors Michael J. Fox and Alan Alda, singer Linda Ronstadt, and civil rights activist Jesse Jackson.

What Are the Symptoms of Parkinson's Disease?

Common motor symptoms include:

Tremors or shaking in hands, arms, legs, jaw, and face
Rigidity or stiffness of limbs and trunk
Slowness of movement
Difficulties with balance, speech, and coordination

There are also non-motor symptoms which may develop years before the onset of motor problems, which may include:

Constipation
Cognitive impairment
Depression
Fatigue
Poor sense of smell
REM sleep behavior disorder (dream-enacting behavior)

Disease warning signs, such as tremors, loss of grip strength, and gait disruption, begin gradually and typically worsen over time. Symptoms and their progression may vary. Parkinson's disease cannot be cured, but treatments and drugs can help control it.

What Causes Parkinson's Disease?

The exact cause of Parkinson's disease is unknown. Most people diagnosed with Parkinson\u2019s have a late-onset form of the disease, which does not have a clear genetic cause. Early-onset Parkinson's, defined as beginning before age 50, accounts for 2% to 10% of cases. This form may have a genetic cause.

Parkinson\u2019s disease likely results from both genetic and environmental factors, and interactions among these factors. A full understanding of Parkinson's risk requires integrated efforts to study both genetic and environmental factors.

Environmental toxicants could cause stress and damage to cells, triggering inflammation in the brainstem.
These exposures could impair mitochondria, the structures within cells responsible for producing energy, and accelerate aging in the brain.
Toxicant exposure may also trigger widespread accumulation of a misfolded version of protein called alpha-synuclein, which is toxic to nerve cells and a hallmark of Parkinson\u2019s disease.

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\n Parkinson's patients have less dopamine. \n

Studies have shown that the symptoms of Parkinson's usually appear when 50% or more of the dopamine neurons in the midbrain are lost. It progresses slowly as small clusters of neurons in the middle of the brain die. The gradual loss of these neurons results in reduction of a chemical called dopamine, which is responsible for transmitting messages to parts of the brain that coordinate muscle movement.

Decades of research suggest several biological processes could drive the nerve cell death seen in Parkinson\u2019s disease.

Parkinson\u2019s disease destroys nerve cells in the brain, yet some researchers think it may start in the gut. Abnormal clumps of misfolded alpha-synuclein proteins have been found in the intestines of people with Parkinson\u2019s disease. These clumps may cause nearby proteins to misfold and clump as well, triggering a chain reaction that travels all the way up the vagus nerve that connects directly to the brain.

There is a critical need for research investment that leads to better understanding of Parkinson\u2019s disease. Identifying environmental exposures related to the onset of Parkinson\u2019s may lead to new prevention and intervention strategies.