Parkinson’s Disease, Essential Tremor, and Genetics
If you or a family member suffers from Parkinson’s disease (PD) or Essential tremor (ET), you may be wondering: How did I end up with this? Will my children end up with PD or ET? Is there a gene that causes PD or ET?
PD is a progressive movement disorder that causes shaking, stiffness, and gait and balance difficulties, amongst other symptoms. Likewise, ET is a progressive neurological disorder that causes shakes to the head, neck, arms, legs, and trunk.
The truth is, the exact cause of PD and ET is unknown. Scientists and researchers believe that these progressive movement disorders result from a combination of genetic and environmental factors. Genetics is said to cause or contribute to 10-15% of all PD cases. Similarly, genetics is said to cause about 17-50% of all ET cases.
Let’s take a deeper dive into the genetics associated with PD and ET.
Understanding the genetics associated with any disease can help you to understand how you may have inherited it, and your chances of passing it on to children or grandchildren in the future.
Let’s start with PD
Understanding the connection between PD and genetics can help us to understand how the disease develops, which helps us determine how to best treat it. There are certain ethnic groups that are more likely to carry the genes that have been linked to PD, including Ashkenazi Jews and North African Arab Berbers. Scientists have discovered a long list of genes associated with PD, but there are 5 main players: SNCA, PARK2, PARK7, PINK1, and LRRK2. Some of those genes (LRRK2, SNCA) are autosomal dominant, meaning that you likely inherited PD from just one parent, as only one copy of the gene has to be altered for the disorder to be expressed. Alternatively, the PARK2, PARK7, and PINK1 genes are said to be inherited in an autosomal recessive pattern, meaning you likely inherited an altered gene from each of your parents. In this instance, it is possible that neither of your parents ever experienced any signs of Parkinson’s disease themselves.
However, just because you possess a gene linked to PD, it does not necessarily mean you will ever end up with PD. In general, if one of your parents has PD, there is a 50% chance that you will inherit a gene associated with PD, and if you do inherit a gene associated with PD, there is a 30% chance that you will end up with the disease.
Now, let’s take a look at the genetics associated with ET.
When ET is inherited from a family member, it is said to be a Familial tremor. In most affected families, ET is inherited in an autosomal dominant pattern - meaning one copy of the altered gene from either parent is enough to cause the disorder. Thus, if you have a parent with a genetic mutation associated with ET, you have a 50% chance of inheriting that gene yourself. While the cause of ET remains poorly understood, researchers have identified two genes that may play a major role in the onset of the disease: ETM1 and ETM2.
The image below will help you to understand an autosomal dominant inheritance pattern, vs an autosomal recessive inheritance pattern.
If you are ever curious about how you or one of your family members have ended up with PD or ET, it is a good idea to consult a genetic counsellor. Genetic counsellors are professionals who are trained to interpret genetic test results, and determine the risks associated with those results. From there, genetic counsellors can help you to make an informed decision about how to proceed with treatments or other options.
In all, understanding the genetic links associated with PD and ET can help us to better understand these diseases, and determine what treatment option might be most beneficial. Thankfully, there are various treatments, medications, and assistive devices available today which can help to minimize the symptoms associated with PD or ET. For example, the Steadi-Two — an assistive device designed to reduce hand tremors for people with Parkinson’s disease and Essential tremor. If you are interested in learning more about the Steadi-Two, click here.