Is Parkinson’s disease genetic?
C. Sort of
D. All of the above
The correct answer, (this being the wacky disease that is Parkinson’s), is of course, “D”, All of the Above.
Parkinson’s disease is not (usually) genetic like, say, Huntington’s disease (what Woody Guthrie had). With that wretched disease, if you have it, you pass on the baddie gene to your kids. Any child of an affected person typically has a 50% chance of inheriting Huntington’s disease. With Parkinson’s, for a very small subset, the disease is caused by a genetic mutation. For example, in people with young onset PD (those in their 20s, 30s and 40s), sometimes the disease is caused by mutations in the parkin gene. (Note to self: Having a gene mutation named after you is usually not a good thing.)
But generally, Parkinson’s is not genetic. Dr. James Beck, Director of Research at Parkinson’s Disease Foundation, writes, “Nearly 90 percent of the people with PD do not have a clearly attributable genetic cause to their disease.”
What got me thinking about genetics as a blog topic was meeting someone who had done genetic testing through a website called “23andme“. Genetic testing used to be a big honking expensive deal, but now, you can just send ’em some spit, plunk down your $99, and poof! all sorts of genetic results. However, for assessing your risk of Parkinson’s, a genetic test isn’t particularly helpful. Dr. Beck goes on to say, “Since consumer testing only looks at a handful of the known PD genes, the odds of using a consumer test to unveil a personal PD-genetic link are rare.”
The lack of a clear genetic marker for PD doesn’t keep the 23andme folks from reporting their PD “discoveries” on their web site, which I find inadvertently hilarious. My personal favorite: “Those with Parkinson’s were less likely to have sky-dived or had liposuction, but more likely to prefer sweet foods over salty ones.”
So, I get it — PD not genetic except for small subset — right? Nope. (Hence, the “sort of” answer above.) There is a new approach to genetic research now: rather than just focusing on singular baddie genes, researchers are also looking at the combination of genes. The $10 phrase is “genome wide association studies”. Scientists suspect that common genetic variants which contribute to the development of, but do not cause Parkinson’s, may increase a person’s overall risk for Parkinson’s if the person has several of these variants.
A major study in 2011 studied the genetic information of more than 12,000 people with PD and some 21,000 healthy individuals. The study concluded that the 20 percent of people who had the highest number of variations in the 11 genetic locations associated with Parkinson’s were 2.5 times more likely to develop Parkinson’s than the 20 percent who had the lowest number of variations in these 11 areas.
The news release from Parkinson’s Disease Foundation reporting on this study concludes, “Authors of this study suggest Parkinson’s may have a stronger genetic component than previously realized. This signals a shift in thinking about the causes of the disease. Twenty years ago, PD was attributed entirely to environmental causes. Today, most scientists believe that a combination of environmental exposures and underlying genetic susceptibility leads to PD in most cases. “