Our genes shape the way we look and how our bodies work, and looking at specific genes or snippets of DNA can offer scientists a glimpse of the control panels for many different physical traits. But researchers are still piecing together the relationship between genes and behavior, and indeed, little is known about how certain types of genes can influence human psychology.
Recently, a rare disorder known as Prader-Willi syndrome (PWS) gave scientists an unprecedented opportunity to pinpoint the location of certain genetic activity associated with paranoia, a mental condition that frequently occurs in people with PWS.
Many traits found in people with PWS — including paranoia — are associated with anomalies in two genes on a single chromosome. In a new study, scientists investigated the genetic makeup of people with the syndrome, noting which individuals exhibited more signs of paranoid behavior and looking for patterns in gene expression, which is the activation of information coded in a gene, to shape a particular trait.
Then, they examined genetic data and questionnaires from 831 people who did not have PWS. Their findings targeted a gene location common among those individuals who reported experiencing paranoia, researchers reported. [The 10 Most Stigmatized Mental Health Disorders]
Previous research has linked genetics to specific behaviors, such as a genetic mutation that was found to influence a person's tendency to be a "night owl." Other studies suggested that a certain genetic marker is responsible for thrill-seeking in skiers, and that impulsivity and addiction in men is associated with a single gene called NRXN3.
However, connecting human behavior to specific genes is extremely challenging. Typically, many genes work together to shape how we behave, and each gene has a relatively small effect, "which makes it difficult to pick out the signal from the noise," the new study's lead author Bernard Crespi, a professor of evolutionary biology at Simon Fraser University in British Columbia, Canada, told Live Science.
The signal in the noise
PWS is caused by anomalies in genes on chromosome 15, and these abnormalities occur randomly during fertilization or fetal development, according to the National Institutes of Health (NIH). The syndrome can cause cognitive impairment and hamper normal growth, and is often characterized in teens and young adults by high rates of psychosis and "schizophrenia-related traits," particularly paranoia and hallucinations, the study authors reported.
As PWS was already associated with paranoid behavior, the researchers determined that there was likely a connection between expressions of paranoia and the unusual genetic activity on that chromosome. They suspected that if they looked at the same genome region in people who did not have PWS but who showed signs of paranoia, that could indicate a location for the genetic activity linked to that psychological state, Crespi said.
What they discovered was "surprisingly specific," Crespi said. A genetic variation known as "SNP rs850807" was strongly associated with aspects of paranoia in people with PWS, but not with other psychological characteristics that frequently accompany the disorder, including traits related to schizophrenia. And in the subjects without PWS who filled out the questionnaire, this genetic variation correlated with paranoid thinking, including beliefs that others "are talking about me," "are watching me," or "have it in for me," the study authors found.
The scientists' findings also offer a new perspective on studying paranoia and "persecutory delusions" [unfounded fear of being harmed] in individuals who are not suffering from PWS, Crespi told Live Science.
"Once you know the genetics you can do imaging. You can localize brain circuits that are active in paranoid ideation. That gives you a much better idea of how the whole paranoia system works," he said.
The findings were published online today (Jan. 17) in the journal Biology Letters.
Original article on Live Science.