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ARE YOU A THRILL SEEKER??
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Vegas EXtreem Skydiving: http://www.vegasextremeskydiving.com/
ACCORDING TO POPULAR PRESS......
People who crave thrills such as skydiving and whitewater rafting may have a genetic basis for this behavior. Researchers have linked the "novelty seeking," or craving exciting new experiences, personality trait to a gene on chromosome 11. According to an article in Time magazine, this was "the first time a normal personality trait [was] firmly linked to a particular gene" (Toufexis, 1996). Personality questionnaires and blood tests were used to assess the relationship between novelty seeking and the D4DR gene. The gene helps in the regulation of dopamine, a chemical mediator for pleasure and emotion in the brain. The subjects characterized as novelty seeking have a longer version of the D4DR gene compared to those who are more reserved. Cells react more strongly to the longer version of the gene when a molecule of dopamine arrives at a cell. Researchers suspect that there are four or five other dopamine related genes involved in determining what compels people to crave excitement. Also, environmental factors like upbringing and opportunity naturally play a role in a person's behavior.
WHAT THE RESEARCHERS HAVE TO SAY.....
As much as 30-60% of variance in personality traits is due to inherited factors according to twin and adoption studies. Researchers have made associations between a long allele of polymorphic exon III repeat sequence in the D4 dopamine receptor gene and the novelty seeking personality trait. The relationship between the gene and trait is supported by studies showing:
- the number of exon III repeats affects the binding of ligands to the receptor
-D4DR is expressed in limbic areas that are involved in emotion and cognition
-in experimental animals, dopamine mediates exploratory behavior
-the rewarding affects of cocaine and amphetamines are related to dopamine release
-novelty seeking is low in dopamine-deficient patients with Parkinson's disease
The gene/trait relationship was investigated in siblings, other family members and individuals in the United States. The family studies showed that the association between long alleles of exon III and novelty seeking personality traits is the result of genetic transmission and not merely population stratification (when subpopulations have different frequencies of the polymorphism and also differ in average phenotype). The results indicate that the novelty seeking trait is partly but not completely mediated by genes, and the D4DR polymorphism accounts for some of the genetic effects but not all (Benjamin et al., 1996).
DO THEY COME TO THE SAME CONCLUSIONS?
Time Magazine and Nature Genetics appear to report the same conclusions concerning the D4DR gene. Naturally, the popular press left out a few of the interesting details concerning the actual experiment, particularly the subjects and how they were tested. This is an acceptable oversight considering the authors probably had a word limit. Popular press does seem to exaggerate the effects of the gene, jumping right to the conclusion that the D4DR gene is responsible for making people want to bungee jump or skydive. Whereas, in Nature Genetics, researchers never use the word "thrill" but rather describe the trait as characterized by "exhilaration or excitement in response to novel stimuli." Both articles do propose the idea that the D4DR gene is not alone in creating the novelty seeking gene, which is important for readers to understand.
SINCE THE INITIAL DISCOVERY.....
-The D4 receptor polymorphism has been described as accounting for only a small percent of the variance in the novelty seeking trait, which suggests that additional genes influence this behavior. (Ebstein et al., 1997)
-A study assessing the association between novelty seeking and D4DR gene polymorphism in the Japanese population suggests that there is an assocaition regardless of racial differences. (Ono et al., 1997)
-Some forms of the polymorphic D4DR may represent a genetic susceptibility factor for Parkinson's Disease. (Ricketts et al., 1998)
-The structure of D4DR has been maintained during primate evolution according to studies with the higher non-human primates. (Inoue et al., 1998)
-A recent study found no significant association between D4DR polymorphisms and novelty seeking. (Herbst et al., 2000)
Benjamin, Jonathan; Li, Lin; Patterson, Chavis; Greenburg, Benjamin D.; Murphy, Dennis L.; Hamer, Dan H. Population and familial association between the D4 dopamine receptor gene and measures of novelty seeking. Nature Genetics. 1996. 12 (1): 81-84.
Ebstein, Richard P.; Novick, Olga; Umansky, Roberto; Priel, Bearice; Osher, Yamima; Blaine Darren; Bennett, Estelle R.; Nemanov, Lubov; Katz, Miri; Belmaker, Robert H. Dopamine D4 receptor (D4DR) exon III polymorphism associated with the human personality trait of novelty seeking. Nature Genetics. 1996. 12 (1): 78-80.
Herbst, Jeffrey; Zonderman, Alan B.; McCrae, Robert R.; Costa, Paul T. Jr. Do the dimensions of the temperamentand character inventory map a single genetic architecture? Evidence from molecular genetics and factor analysis. American Journal of Psychiatry. August 2000. 157 (8): 1285-1290.
Inoue, Marayama Miho; Takenaka, Osamu; Murayama, Yuichi. Origin and divergance of tandem repeats of primate D4 dopamine receptor genes. Primates. April 1998. 39 (2): 217-224.
Ono, Yutaka; Manki, Hiroshi; Yoshimura, Kimio; Muramatsu, Taro; Mizushima, Hiroko; Higuchi, Susumu; Yagi, Gohei; Kanba, Shigenobu; Asai, Masahiro. Association between dopamine D4 receptor (D4DR) exon 3 polymorphism and novelty seeking in Japanese subjects. American Journal of Medical Genetics. 1997. 74(5): 501-503.
Ricketts, Michael H.; Hamer, Robert M.; Manowitz, Paul; Feng, Fei; Sage, Jacob I.; Di, Paula Rocco; Menza Matthew A. Association of long variants of the dopamine D4 receptor exon 3 repeat polymorphism with Parkinson's disease. Clinical Genetics. July 1998. 54 (1): 33-38.
Toufexis, Anastasia. What makes them do it? Time. January 15, 1996. 60.
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