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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Parkinson disease

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* Not a rare disease
Other Names for this Disease
  • Paralysis agitans
  • Parkinson's disease
  • Primary parkinsonism
  • Shaking palsy
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Your Question

The woman I would like to marry has a family history of Parkinson disease. How is this condition inherited? How is it diagnosed? Is genetic testing available?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is Parkinson disease?

Parkinson disease belongs to a group of conditions called movement disorders. The four main symptoms are tremor, or trembling in hands, arms, legs, jaw, or head; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance. These symptoms usually begin gradually and worsen with time.  As they become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks.  Not everyone with one or more of these symptoms has Parkinson disease, as the symptoms sometimes appear in other diseases as well.[1] Parkinson disease affects about 1 to 2 percent of people over the age of 60 years and the chance of developing Parkinson disease increases as we age.[2] Although some Parkinson disease cases appear to be hereditary, and a few can be traced to specific genetic mutations, most cases are sporadic and occur in people with no apparent history of the disorder in their family.  Many researchers now believe that Parkinson disease results from a combination of genetic susceptibility and exposure to one or more environmental factors that trigger the disease.[1] 
Last updated: 10/3/2011

What causes Parkinson disease?

Parkinson disease occurs when the nerve cells in the brain that make dopamine, a chemical messenger which transmits signals within the brain to produce smooth physical movements, are slowly destroyed. Without dopamine, the nerve cells in the part of the brain known as the substantia nigra cannot properly send messages. This leads to progressive loss of muscle function. Exactly why these brain cells waste away is unknown.[1][3] Recent studies have shown that people with Parkinson disease also experience damage to the nerve endings that produce the neurotransmitter norepinephrine. Norepinephrine, which is closely related to dopamine, is the main chemical messenger of the sympathetic nervous system, the part of the nervous system that controls the automatic functions of the body, including pulse and blood pressure. The loss of norepinephrine may explain some of the non-motor features seen in Parkinson disease, including fatigue and problems with blood pressure regulation.[1] 

More detailed information about the cause of Parkinson disease is available through an information page developed by the National Institute of Neurological Disorders and Stroke (NINDS). Click here to view this information.

Last updated: 10/3/2011

Is Parkinson disease inherited?

Most cases of Parkinson disease are classified as sporadic and occur in people with no apparent history of the disorder in their family. Although the cause of these cases remains unclear, sporadic cases probably result from a complex interaction of environmental and genetic factors. Additionally, certain drugs may cause Parkinson-like symptoms.[4]

Approximately 15 percent of people with Parkinson disease have a family history of the disorder. These familial cases are caused by mutations in the LRRK2, PARK2, PARK7, PINK1, or SNCA gene, or by alterations in genes that have not yet been identified. Mutations in some of these genes may also play a role in cases that appear to be sporadic.[4]

It is not fully understood how mutations in the LRRK2, PARK2, PARK7, PINK1, or SNCA gene cause Parkinson disease. Some mutations appear to disturb the cell machinery that breaks down (degrades) unwanted proteins. As a result, un-degraded proteins accumulate, leading to the impairment or death of dopamine-producing neurons. Other mutations may involve mitochondria, the energy-producing structures within cells. As a byproduct of energy production, mitochondria make unstable molecules, called free radicals, that can damage the cell. Normally, the cell neutralizes free radicals, but some gene mutations may disrupt this neutralization process. As a result, free radicals may accumulate and impair or kill dopamine-producing neurons.[4]

In some families, alterations in the GBA, SNCAIP, or UCHL1 gene appear to modify the risk of developing Parkinson disease. Researchers have identified some genetic changes that may reduce the risk of developing the disease, while other gene alterations seem to increase the risk.[4]

Last updated: 10/3/2011

How do people inherit Parkinson disease?

Most cases of Parkinson disease occur in people with no family history of the disorder. The inheritance pattern in these cases is unknown. Among familial cases of Parkinson disease, the inheritance pattern differs depending on the gene that is altered. If the LRRK2 or SNCA gene is involved, the disorder is inherited in an autosomal dominant pattern, which means one copy of an altered gene in each cell is sufficient to cause the disorder. Parkinson disease is inherited in an autosomal recessive pattern if the PARK2, PARK7, or PINK1 gene is involved. This type of inheritance means that two copies of the gene in each cell are altered. Most often, the parents of an individual with autosomal recessive Parkinson disease each carry one copy of the altered gene but do not show signs and symptoms of the disorder.[4]

The inheritance pattern is unclear when an increased risk of Parkinson disease or parkinsonism is associated with mutations in the GBA gene. SNCAIP and UCHL1 mutations have been identified in just a few individuals. It is unclear how these mutations are related to Parkinson disease, and the inheritance pattern remains unknown.[4]

Last updated: 10/3/2011

How is Parkinson disease diagnosed?

There are currently no blood or laboratory tests that have been proven to help diagnose sporadic cases of Parkinson disease. The diagnosis is generally made after careful evaluation of medical history, current symptoms, and exclusion of other conditions.[1] The clinical findings of tremor, rigidity, and bradykinesia are highly suggestive of Parkinson disease. The genetic cause of some forms of Parkinson disease has been identified. In those cases, genetic testing may be utilized to identify affected family members.[5]
Last updated: 10/3/2011

Is genetic testing available for Parkinson disease?

GeneTests lists laboratories offering clinical genetic testing for the HTRA2-related, LRRK2-related, PARK7-related, PINK1-related, Parkin, and SCNA-related types of Parkinson disease. Clinical genetic tests are ordered to help diagnose a person or family and to aid in decisions regarding medical care or reproductive issues. Individuals and families who are interested in having genetic testing can learn more about their risk for Parkinson disease and the availability and accuracy of genetic testing for this disease by setting up an appointment with a genetics professional.
Last updated: 10/3/2011

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 10/18/2013

References