When people are diagnosed with Parkinson's disease, they often want to know if it's hereditary. Can their kids get it? Are their grandchildren at risk? Well, the answer is complicated.
"Most of the time we don't know what is really causing the disease in people," Irene Litvan, MD, director of the Movement Disorders Center at the University of California, San Diego, tells Health.
Is-Parkinson's-Disease-Hereditary-GettyImages-154455875-AdobeStock_189624167 . But just because you have a mutation on a certain gene or a relative with Parkinson's doesn't mean you're definitely going to get the disease. Experts agree that a combination of factors (age, environment, and yes, genetics) contribute to the disease, but the extent to which each factor impacts a person varies from case to case.
Let's take a closer look at the genetic factors associated with Parkinson's disease and just how hereditary the disease really is.
Is Parkinson’s considered a hereditary disease?
Nope, Parkinson's isn't considered a hereditary disease in most people. According to the Parkinson's Foundation, about 90% of people with the disease have no genetic link.
And while there are some genetic markers for Parkinson's, they don't guarantee that a person will get the disease. A genetic mutation is just one of several risk factors for Parkinson's disease. There may also be lifestyle choices and environmental factors involved in the development of the disease. In fact, most people with Parkinson's disease aren't aware of any other family member with the condition, according to the National Human Genome Research Institute (NHGRI).
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In rare cases, Parkinson's disease can run in families. When three or more relatives get the disease—especially under the age of 50, which is considered early onset—experts believe members of the family may have a genetic predisposition to Parkinson's.
How hereditary is Parkinson’s disease?
There are two categories of genetic factors linked to Parkinson's. The first is "causal," meaning the gene itself is capable of bringing on the disease. (This kind of genetic predisposition to Parkinson's is super rare, accounting for less than 2% of Parkinson's disease cases.)
One example of a causal link to Parkinson's disease can be found in the SNCA gene. Researchers know of at least 30 mutations on this particular gene that can cause Parkinson's disease, especially in people younger than 50 years old.
The SNCA gene tells the body how to make a protein called alpha-synuclein. When the gene has a mutation, the body may produce too much alpha-synuclein or versions of the protein with an incorrect shape. Either of these problems can lead to alpha-synuclein to gather in the brain in clusters called Lewy bodies, which disrupt normal brain functioning. Lewy bodies are associated with Parkinson's, along with a range of other diseases (including the type of dementia that affected Robin Williams).
Not all genetic mutations cause Parkinson's disease, though. "Associated" genetic factors for Parkinson's increase a person's odds of developing the disease, but aren't directly responsible for it.
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"You're susceptible, but you need something else present as well [to actually get the disease]," Dr. Litvan says. "That could be other genes or it could be an environmental factor."
An example of an associated Parkinson's gene is LRRK2. There are at least 20 different LRRK2 mutations linked to Parkinson's, according to the Parkinson's Foundation, and they can be found in up to 2% of all people with Parkinson's disease. Mutations on this gene can lead to the loss of neurons (which play a role in helping the brain store memories). Rates of mutations on the LRRK2 gene tend to be higher among individuals who are of Ashkenazi Jewish, Basque, and North African Berber descent, which can put them at increased risk for Parkinson's disease.
Then there are mutations on the GBA1 gene, which has recently emerged as the most common genetic abnormality linked to Parkinson's disease. (Approximately 5% of people with Parkinson's disease patients carry a GBA1 mutation, in comparison to less than 1% of people who don't have the disease.) Mutations on this gene can affect the ability of a person's cells to break down toxic substances, get rid of certain bacteria, and dispose of worn-out material. That, in turn, may cause Lewy bodies to form in the brain.
There are many other genetic mutations that have been linked to Parkinson's, and ongoing research may continue to uncover other markers for the disease.
With all that said, most people with genetic mutations associated with Parkinson's never actually get the disease. The Parkinson's Foundation explains that this disease is "a result of a complex interaction between genes and environmental factors." So, while it can be helpful to be aware Parkinson's genetic factors in some situations, you don't need to panic if you have one of these genetic mutations.
Should I get tested for genetic markers for Parkinson’s?
You can find out if you have certain genetic markers for Parkinson's disease with at-home genetic tests. However, Dr. Litvan is cautious about recommending genetic testing for everyone. Remember: Most people with the mutations linked to Parkinson's never get the disease, so you may end up with a ton of unnecessary stress and worry if your results reveal one of these genetic factors.
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Generally speaking, you should consider testing for genetic markers for Parkinson's if you have a family history of the disease, says Lynda Nwabuobi, MD, an assistant professor of clinical neurology at Weill Cornell Parkinson's Disease and Movement Disorders Institute.
"If I see a patient who comes in and they have Parkinson's, their mother had Parkinson's, their maternal grandparents had Parkinson's, or they also have another sibling who has Parkinson's, there's clearly some family history," she tells Health. "And to those individuals, I'll say, 'Let's get you genetic testing.'"
By getting tested, people with Parkinson's (or with a family history of it) can give scientists more information to work with in the grand scheme of medical research—and potentially tee themselves up for access to groundbreaking medicine.
"If you're someone who has, let's say, the GBA gene, and in five years [a treatment] comes out that's specific for patients with that gene, you would want to know, right?" Dr. Nwabuobi says. "So that's a good reason to get tested."
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