Parkinson's disease is the second most common neurodegenerative condition after Alzheimer's, with nearly one million Americans living with the disease and ten million people affected worldwide.
With genetic testing now available, people with Parkinson's and their families are increasingly turning to testing to learn more about their disease and if their children are at risk.
"Genetic testing can be useful, but the information can be overwhelming or even misleading."
Which test to take and how to interpret the results, though, can be confusing. "Getting genetic testing can be useful, but the information can be overwhelming or even misleading," says neurologist Roy Alcalay, MD, an expert in the treatment of Parkinson's at Columbia and NewYork-Presbyterian who also studies the genetics of the disease.
"That why it's best to couple any testing with genetic counseling. Getting genetic testing is pretty profound, because people receive a lot of potentially positive or negative information. Without a genetic counselor to prepare you and explain the results, I would advise against genetic testing," says Alcalay.
Tests vary
The genetics of Parkinson's disease is complex, and risk cannot be determined by looking at the presence or absence of a single gene.
Genetic testing for Parkinson's emerged in the 2000s after the identification of the first known disease-causing variants. Currently, researchers think about 90 genes may be contribute to Parkinson's disease.
But tests vary widely, complicating interpretation and counseling.
"If one company examines five genes and another examines 62, are they offering the same product? Is the result the same, and what do you do with it?"
Clinical laboratories worldwide currently offer more than 500 unique clinical genetic tests for Parkinson's, with tests examining anywhere from five to 62 genes, according to a recent study by Alcalay, neurologist Karen Marder, MD, a Parkinson's expert at Columbia and NewYork-Presbyterian, and other colleagues. Many tests include genes whose connection to Parkinson's is still controversial among scientists.
"This makes it very confusing both for people with Parkinson's and for providers, because if one company examines five genes and another examines 62, are they offering the same product? Is the result the same, and what do you do with it?" Marder says.
Where to start?
One way to access testing is to join the PDGENEration study, a flagship initiative of the Parkinson's Foundation, for which Alcalay is the lead investigator. Study participants are provided pre- and post-test counseling and genetic testing for mutations in the most common Parkinson's genes. The study is designed to help accelerate clinical trials of gene-specific therapies and improve patient care. Alcalay says about 3,500 people have already completed the study, which can accommodate 15,000 people.
Direct-to-consumer genetic testing is also available but may not involve a genetic counselor to prepare test-takers and interpret the results.
"Before taking a genetic test, it's important for counselors to help people imagine the worst-case scenario, so they can process how they might feel," says Marder.
"Take your time making a decision about testing, because once you have that information, you can't take it back."
A genetic counselor also explains the ambiguity associated with test results. "Just because somebody has a genetic mutation associated with Parkinson's, that doesn't necessarily mean they will develop Parkinson's," Marder says. Factors such as diet and exercise could possibly postpone development of the disease.
Many people are eager to have genetic testing, including children of Parkinson's patients who want to know their risk. Marder and Alcalay know of several who started the testing process but chose not to receive results after meeting with the genetic counselor.
"The family dynamics can be quite nuanced. Some parents with Parkinson's undergo testing, but then are faced with a decision about giving their children unpleasant news. Or a child who learns she did not inherit a parent's Parkinson's gene may feel conflicted about sharing that with an affected family member," Marder adds.
"Take your time making a decision about testing, because once you have that information, you can't take it back."
References
Roy Alcalay, MD, is associate professor of neurology at Columbia University Vagelos College of Physicians and Surgeons and an attending physician at NewYork-Presbyterian.
Karen Marder, MD, is the Sally Kerlin Professor of Neurology at Columbia University Vagelos College of Physicians and Surgeons and an attending physician NewYork-Presbyterian.
