Alternative Names
Parkinson Disease; Primary Parkinsonism; PD
Symptoms & Characteristics
Parkinson's disease is a nervous system disorder that affects nerve cells in a part of the brain that controls muscle movement. Normally, these neurons produce a chemical messenger called dopamine, which send signals to produce smooth physical movements. In Parkinson's disease, these dopamine-producing-neurons die or do not work properly.
This breakdown in communication between the brain and muscles cause the muscles to weaken, and eventually, the brain is unable to control muscle movement. Symptoms of the disease usually begin around 60 years old, but can start even earlier. Symptoms can include:
- trembling of hands, arms, legs, jaw and face
- stiffness of the arms, legs and trunk
- poor balance and coordination
As symptoms worsen, people with the disease may have trouble walking, talking or doing simple tasks. They may also have problems such as depression, sleep problems or trouble chewing, swallowing, or speaking.
Parkinson's disease can run in families with more than one affected family member, called familial Parkinson's disease, but typically strikes at random with no family history, called sporadic Parkinson's disease. Both types of Parkinson's disease are clinically similar; however, some people with familial Parkinson's disease have early-onset Parkinson's disease (symptoms begin before 50 years old) or juvenile-onset Parkinson's disease (symptoms begin before 20 years old).
Treatment
There is no currently no cure for Parkinson's disease. Medications and treatment may relieve some symptoms.
How Common Is It?
About 1 million people in North America and more than 4 million people worldwide are affected with Parkinson's disease. More men than women are typically affected.
Genetics & Inheritance
Most people
with Parkinson's disease have sporadic Parkinson's disease. The cause of sporadic Parkinson's disease is largely unknown. Parkinson's disease is most likely a multifactorial condition, which means that it involves a combination of genetic, lifestyle and environmental factors.
- Some environmental factors that have been proposed to possibly influence Parkinson's disease risk include certain drugs, head trauma, and pesticide use.
About 15% of people with Parkinson's disease have familial Parkinson's disease, which is caused by an inherited genetic mutation.
In addition to the above genes, growing evidence suggests an association between GBA mutations (location 1q21) and Parkinson's disease or Parkinson-like disorders that affect movement and balance (parkinsonism). The GBA gene is most commonly associated with Gaucher disease, a genetic condition that affects various parts of the body. We all have two copies of the GBA gene, one from each parent. Individuals with Gaucher disease have two mutations, one in each gene copy. People with a mutation in just one gene copy are called carriers and typically do not have symptoms of Gaucher disease. Some studies suggest that both individuals who are afffected with Gaucher disease and individuals who are carriers have an increased risk of developing Parkinson's disease or parkinsonism.
Mutations in a number of other genes, such as NR42A and SNCAIP, appear to modify (reduce or increase) the risk to develop Parkinson's disease.
Researchers believe mutations in some of the genes that cause familial Parkinson's disease may also play a role in cases that appear to be sporadic and not inherited.
In addition to the known disease-causing mutations, some researchers have identified small genetic variations that may influence the risk to develop Parkinson's disease in some people. Researchers have proposed that certain single nucleotide polymorphisms (SNPs), which are small variations in a single "letter" of DNA that can be found throughout our entire genetic make-up, may cause susceptibility to Parkinson's disease. However, the exact mechanisms in which these SNPs contribute to Parkinson's disease risk is unclear. Further research is needed to replicate study findings across different ethnic groups and clearly establish associations.
The inheritance pattern of familial Parkinson's disease varies by gene.
- In the LRRK2, UCHL1 and SNCA genes having a mutation in a single gene copy is sufficient to cause the disease. However, not every person who has a mutation will develop physical symptoms in their lifetime. This is called autosomal dominant inheritance with incomplete penetrance. Every person with a mutation has a 50% chance to pass on their mutation to each child they have.
- In the PARK2, DJ-1, or PINK1 genes, it is usually necessary to have two mutations, one in each copy, to be affected. This is called autosomal recessive inheritance. Both parents of an affected person are always obligate carriers (each have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but typically do not have symptoms themselves.
- Of note, some people with only one identified PARK2 mutation have been affected. This raises an issue. In some cases, one mutation in this particular gene may be sufficient to cause disease or increase the risk of disease.
There are other conditions that have symptoms which overlap with Parkinson's disease. Some of these conditions include Huntington's disease and Alzheimer's disease. A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of testing and recurrence risk.
Genetic Testing
Clinical genetic testing for some of the genetic causes of familial Parkinson's disease may be available
through an in person genetic consultation for people who are considered at risk.
Use our find a genetic professional directory to locate a trained genetic professional
in your area.
Informational genetic testing for susceptibility to Parkinson's disease is available online (over the internet). Informational genetic testing for susceptibility to Parkinson's disease is also available as part of a whole genome scan. Whole genome scanning involves analyzing thousands of SNPs at once related to a number of different health conditions.
- At this point, many genetic professionals do not consider this testing clinically useful or medically relevant, but for informational purposes only. Go to the Tests tab to link to the best providers, compare providers and read provider reviews.
Support & More Information
More information can be
found at:
Support can be found at:
Last Reviewed November 16, 2009