Report Links Gene Variation to Novelty-Seeking Trait
One specific kind of genetic variation makes people more likely to be excitable, fickle, thrill seeking and quick-tempered, according to two studies published today. If confirmed by further research, that association would be among the first found between a gene that affects brain chemistry and a normal aspect of personality.
Two independent groups of scientists, working in different countries and using different methods, report the same results in today’s issue of the journal Nature Genetics: Individuals who have a certain kind of extra-long DNA sequence on part of Chromosome 11 also score much higher on psychological tests measuring a personality trait called “novelty seeking.”
The parallel sets of findings are “intriguing,” said Elliot Gershon, chief of clinical neurogenetics at the National Institute of Mental Health, although the genetic effect on personality has not been established conclusively. Nonetheless, he said, “the idea that we can find specific genes that affect normal human behaviors--as opposed to mental illness--is very important.”
“This is major news,” said psychologist Brian Gladue, who studies the biology of behavior at the Institute for Policy Research at the University of Cincinnati. “This is going to open up a whole new field of molecular personality research.”
Many researchers have noted that genetic contributions to mental illness cannot be completely understood unless scientists also determine how genes influence ordinary personality characteristics. If such connections can be demonstrated, “success in mapping genes for a normal personality trait may signal a fruitful way to map genes for psychopathology as well,” Washington University brain researcher C. Robert Cloninger and colleagues write in an accompanying commentary in the journal.
Both of the new studies set out to test the hypothesis, advanced by Cloninger, that novelty-seeking behavior is affected by the way brain cells process a neural messenger chemical called dopamine. The way that chemical message is transmitted is determined, in large measure, by a gene called D4DR that controls the formation of a dopamine receptor.
There are various alternative forms of that gene, one of which has a particularly long series of seven repeated sequences, and one of which has only four.
Richard P. Ebstein and colleagues at Sarah Herzog Memorial Hospital in Jerusalem examined 124 unrelated Israeli subjects, giving them a test devised by Cloninger that measures four personality dimensions: novelty seeking, harm avoidance, reward dependence and persistence. The researchers also took blood samples from each subject for genetic analysis.
They found that subjects who scored highest on novelty seeking (“characterized as impulsive, exploratory, fickle, excitable, quick-tempered and extravagant”) were much more likely to have the long, seven-segment component of D4DR. Subjects with the shorter version scored significantly lower. (Those who score lower than average on novelty seeking “tend to be reflective, rigid, loyal, stoic, slow-tempered and frugal,” the researchers note.)
The subjects--who were of both sexes, various ages and different ethnic backgrounds--did not differ significantly in any of the test’s other personality categories. In addition, the relationship between the long-sequence DNA component and novelty seeking did not vary with age, sex or ethnicity.
In the second study, conducted by Jonathan Benjamin and his colleagues at the Laboratory of Clinical Science at the National Institute of Mental Health, researchers tested 315 American subjects, most of them male siblings and other family members.
Again, the study found that subjects with long sequences of repeated DNA in their D4DR gene scored higher on such variables as extroversion, excitement-seeking, positive emotions, extravagance and disorderliness. Those with shorter repeat sequences generally scored lower. Again, the genetic difference did not have a significant effect on other personality traits within the subject group.
As scientists discover more individual genes that affect particular traits, it might open the door to identifying people at risk for such problems as drug abuse and then counseling them on how to lower their risk, Ebstein said.
It might also add a twist to the issue of who’s entitled to know about a person’s genetic makeup.
An insurance company might want to know if “genetically, you’re a thrill seeker and enjoy jumping out of airplanes in a skydiving club and taking risks in general,” said Ebstein, director of research at the Herzog Memorial Hospital in Jerusalem.
About 15% of people in Israel, Europe and the United States carry the novelty-seeking form of the gene. But just why it would encourage novelty seeking is still a mystery, Ebstein said.
