The experts at NorthShore Neurological Institute answer questions to help raise awareness about this common and often disabling neurological disorder.

Are the children of a parent with Parkinson’s disease likely to inherit the disease? Is there a greater risk if the father or the mother has the disease?

Our research teams conducted family studies that defined the risk of inheriting Parkinson’s disease. The children of Parkinson’s disease patients carry a two-fold risk for Parkinson’s disease. They are twice as likely to get Parkinson’s disease compared to the children of persons without Parkinson’s disease.

However, one needs to consider that the lifetime risk for Parkinson’s disease in the general population is 2%, so the risk of Parkinson’s disease for the children of a patient is 4%, or twice the baseline risk for the general population. That’s a pretty low risk and I wouldn't recommend any specific lifestyle changes or preventive therapies for the children of patients with Parkinson’s disease.
 
That said, about 5% of Parkinson’s disease cases are due to an inherited gene abnormality (mutation). In families where multiple members have Parkinson’s disease, the risk may be as great as 50% to the children of an affected person. When there are multiple family members with Parkinson’s disease, we refer patients for genetic counseling and in some instances, we also perform genetic testing. 

What are the most important genetic risk factors for Parkinson’s disease?

There are two types of genetic factors that are important to Parkinson’s disease: 1) Genes that rarely cause familial Parkinson’s disease (multiple affected members in the same kindred), and 2) genes that are not causal but that slightly increase the risk for Parkinson’s disease in populations worldwide (susceptibility genes).

About a dozen genes have been identified as rare causes of familial Parkinson’s disease, and about a dozen genes have been identified as common risk factors in populations worldwide. The causal gene mutations are rare, accounting for less than 5% of all Parkinson’s disease cases. The susceptibility gene variants are common—e.g., occurring in 25% of persons in the general population—but they have small effects (no more than doubling the risk for Parkinson’s disease).  

Of all of the Parkinson’s disease genes, the most important is alpha-synuclein because it is both a causal gene in some families and also a susceptibility gene in populations worldwide. In other words, rare variants (mutations) cause Parkinson’s disease in rare families, while common variations (polymorphisms) increase the risk for Parkinson’s disease worldwide.

The alpha-synuclein gene holds the code for making the protein alpha-synuclein. The protein alpha-synuclein accumulates abnormally in the brain cells of every patient with Parkinson’s disease regardless of the causes. Many scientists believe that it holds the key to understanding and curing Parkinson’s disease. Our research team at NorthShore has led many of the most important studies of alpha-synuclein and Parkinson’s disease, including studies in families and in populations worldwide. We were also amongst the first to study the interaction of alpha-synuclein with other genes or environmental factors or to study the association of the alpha-synuclein gene with motor and cognitive outcomes in Parkinson’s disease. 

Are there genetic research studies of Parkinson’s disease at NorthShore? How can I participate?

NorthShore is conducting a genetic study called the DodoNA Project. We aim to discover genetic factors that predict how neurological diseases progress in severity and that predict disease outcomes. We aim to use this information to individualize the care of our patients and to halt the progression of neurological diseases. One of the diseases we are studying is Parkinson’s disease. 

We enrolled at least 1,000 Parkinson’s disease patients into the study, and we're following them at least annually for several years.