Genetics is the science of genes and heredity. It explores how traits are passed from one generation to another through genes, which are made of a molecule called DNA. From time to time, variations called mutations occur as genes are passed on. Scientists believe some of these mutations may be linked to the development of diseases such as Parkinson’s. Genetic research seeks to identify the genes concerned and develop new treatments for genetic illnesses.

Genetic testing is a type of medical testing that identifies changes in genes that may be linked to inherited diseases. The results of these tests can help to confirm or rule out a suspected genetic condition. They may also provide information about the person’s chances of developing or passing on a genetic illness.

Research suggests that a combination of genetic and environmental factors leads to the development of Parkinson’s in most cases. Research continues to determine how these factors interact, and the extent to which each is involved. Current research suggests that only about five percent of cases of Parkinson’s can be definitely linked to a genetic cause.

Although there are a few families in which more than one person develops Parkinson’s, it is rare for the condition to be passed from one generation to the next. Most research suggests that the condition develops as a result of genetic susceptibility and an external trigger, such as environmental chemicals. Exactly how this happens is not yet clear.

Researchers have so far identified a number of genes that seem to be linked to Parkinson’s, including the parkin, PINK1, PARK7, SNCA and LRRK2 genes. It is important to note, however, that a mutation of one of these genes does not necessarily mean that the condition will develop.

Genetic testing for several Parkinson’s genes is now quite widely available. From a medical point of view, this can help to confirm a diagnosis of Parkinson’s. However, the decision to undergo genetic testing needs to be made carefully, as it may have implications for other family members. Knowing there is an increased risk of developing Parkinson’s may cause unnecessary worry in people who may never go on to develop the condition.

If a person is tested and an increased risk is found, regular monitoring may be arranged to detect early signs of the condition. Testing may also be offered to other family members.

Interpretation of test results can be difficult. For example, some carriers of the mutated genes that have been linked to Parkinson’s do not develop the condition. Nor can testing guarantee that a genetically healthy person will not go on to develop Parkinson’s at some point.

As our understanding of the genetic links to Parkinson’s grows, scientists hope to develop reliable tests to identify those who are at risk. This could help with early diagnosis even before symptoms appear. As new treatments and medications are developed, assessment of genetic risk and early diagnosis will become increasingly important so that treatment can begin promptly.

If you want to find out more about genetic testing your doctor should be able to put you in contact with a specialised genetics health professional.

Tests are generally arranged through a healthcare professional who can then interpret the results and give advice on how the information can be used.

Genetic testing is now also available from a number of companies who deal directly with people being tested. This can have several implications:

• Your doctor is not automatically informed of results, allowing you to keep findings to yourself if you wish.
• Results will not automatically be passed to your insurance company, although you should check your policy as you may be required to reveal all genetic test information. Failure to do so could invalidate your cover.
• You may not get the opportunity to discuss your test results and their implications with an experienced healthcare professional.

Important! Thoroughly check the credentials of any company offering genetic testing, as not all provide a high standard of service.

Content last reviewed: February 2018

• VIDEO: Ask the MD: Genetic Testing for Parkinson's Disease (The Michael J. Fox Foundation)
• Navigating Clinical Trials - A Guide for Parkinson’s Patients and Families (The Michael J. Fox Foundation), pp. 29-39: Genetics and Parkinson’s Research