Sensation seeking has been linked to a range of behavior disorders, such as drug addiction. It isn't all bad, though. "Not everyone who's high on sensation seeking becomes a drug addict. They may become an Army Ranger or an artist. It's all in how you channel it," says Jaime Derringer, a PhD student at the University of Minnesota and the first author of the study. She wanted to use a new technique to find out more about the genetics of sensation seeking. Most obvious connections with genes, like the BRCA gene that increases the risk for breast cancer, have already been found, Derringer says. Now new methods are letting scientists look for more subtle associations between genes and all kinds of traits, including behavior and personality.
Derringer used a kind of mutation in DNA called a single-nucleotide polymorphism, or SNP. A SNP is a change in just one "letter" of the DNA.
Note that single letter differences are just one of a few genetic differences possible. But SNPs are cheaper to test for. So they get more research attention.
She started by picking eight genes with various roles related to the neurotransmitter dopamine, which has been linked to sensation seeking in other studies. She looked at group of 635 people who were part of a study on addiction. For each one, she had genetic information on 273 SNPs known to appear in those 8 genes and a score for how much they were inclined to sensation seeking. Using that data, she was able to narrow down the 273 SNPs to 12 potentially important ones. When she combined these 12 SNPs, they explained just under 4 percent of the difference between people in sensation seeking. This may not seem like a lot, but it's "quite large for a genetic study," Derringer says.
Note that the 12 genes suspected of having influence might only explain 4% of the variation in sensation seeking. The emerging picture with genetic variants that influence cognitive processes is that each variant makes only a small contribution. The same has been found in the search for genetic variants that influence intelligence. This highlights the need for very large populations of study subjects in order to discover the signal of very small genetic influences.
In this study the researchers used only used genetic material 635 people. Not enough to discover hundreds of genetic variants that each might contribute a fraction of one percent to the total tendency toward sensation seeking. What's needed are full genetic sequences of hundreds of thousands of people. But that would cost orders of magnitude more to do. Fortunately the cost of genetic testing and genetic sequencing continues to fall by orders of magnitude. So the flood of data needed to tease out of the contributing genetic variants is going to come in the next 5 years. We'll see bigger data sets and larger number of genetic influences identified each year.
|Share |||Randall Parker, 2010 October 06 10:45 PM Brain Genetics|