BY: DORIAN YABLINMENTOR: DR. NANCY ELWESS

The Genetic Analysis of High Risk Athletes for the Presence of the

DRD4 7 Variable Tandem Repeat

Research Goals:

The purpose of this research was to examine the DRD4 tandem repeats within the three experimental groups, and determine if there was a higher rate of DRD4-7 repeats than in the control group.

The three experimental groups: Expeditionary Studies students Olympic level bobsledders Free soloing rock climbers

Research Goals continued:

Because participants have two copies of this gene, their genotype results were based on the presence of the 7 repeat (or more) allele (7+) or absence (7-).

This study was designed to examine the extent to which these tandem repeats appeared in the test controls and hopefully determine if they played a role in the novelty seeking/thrill seeking activities.

Research Goals continued:

The dopamine receptor D4 (DRD4) expresses a polymorphism in exon III; the variants in this exon are caused by allelic variations on the 11th chromosome (Figure 1).

Changing the number of possible repeats on exon III of the D4 receptor alters the length, structure, and the efficiency of the receptor (Sander et al., 1997). DRD4 has ten known repeats between 2 and 11 within this exon. The most common repeats being 2, 4 and 7 (Haradon & Galdzicki, 2015).

Figure 1: Dopamine receptor D4 gene. The 48 bp tandem repeat is located within exon 3. Image generated by Dorian Yablin.

Hypothesis:

That the three experimental groups (expeditionary study majors, international bobsledder, and free soloing rock climbers) would display a statistical higher frequency of 7+ repeats than the control.

Research methods:

Cheek cells were collected from participants using 0.9% saline solution.

Their DNA was then isolated from the solution using the procedures as outlined in Genetic Origins (Cold Spring Harbor Laboratory).

The DRD4 polymorphic genotypes were verified through polymerase chain reaction (PCR) as described in Dreber et al. (2009).

The PCR primers used were: Forward: 5’- GCG ACT ACGTGG TCT ACT CG -3’ Reverse: 5’- AGG ACC CTC ATG GCC TTG -3’.

The PCR products were visualized using ultraviolet fluorescence following migration of samples within 1.2% agarose gels containing ethidium bromide as explained in Lichter et al. (1993).

Research Methods continued:

Statistical Analysis Analysis was done using cross tabulation through

SPSS. Participants were classified according to the presence of (7+) or the absence (7-) of the repeats founds within exon III of the DRD4 gene.

Data and Results:

As the level of risk and experience increased to free soloing rock climbers and Olympic level bobsledders there was a greater amount of individuals expressing one or both 7+ alleles. Overall there was a statistically significantly higher amount of 7+ repeats present when the three experimental groups were combined and compared to the control.

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Data and Results continued:

If this study were repeated, the survey would be more extensive, and would ask individuals about any certifications they have pertaining to these activities. It would also ask about participant’s level of expertise in the sport, not just their willingness to take risk.

Conclusion:

The three experimental groups were chosen specifically for this study based on the amount of risk taking that is associated with each group, and the personalities of the individuals drawing them to participate in higher risk activities.

Conclusion continued:

When analyzing the results, it was unexpected to see such low 7+ repeat results for the Expeditionary Studies group.

In the survey responses, 65% said they would be very likely to take risk when participating in higher risk sports such as rock climbing, or white water kayaking.

After isolating and analyzing the participant’s saliva samples, only 7.69% of the participants contained a single or double allele of the 7+ repeat variant Expeditionary Studies

students taking a lunch break in Scotland, Image by Dorian Yablin

Conclusion continued:

There are many different possibilities as to why the research yielded an insignificant difference between the Expeditionary Studies group, and the control.

What was not taken into consideration during the study was the level of expertise the Expeditionary Studies group had. In the outdoor industry there are various types of certifications awarded to individuals who prove their ability to do certain high-risk sports under different circumstances.

Both the international bobsledders and free soloing rock climbers are competing at the highest level of expertise in their sport. The Expeditionary Studies group is still learning the proper techniques to safely participate in the various high-risk sports.

Acknowledgments:

Thanks to Dr. Thomas Wolosz for his assistance with the statistical analysis.

And to Dr. Nancy Elwess for all of her guidance.

References:

Cold Spring Harbor Laboratory. Genetic Origins. Retrieved on January 19, 2016 from: http://www.geneticorigins.org/mito/mitoframeset.htm

Dreber, A., Apicella, C.L., Eisenberg, D.T.A., Garcia, J.R., Zamore, R.S., Lum, J.K., and Campbell, B. (2009). The 7R polymorphism in the dopamine receptor D4 gene (DRD4) is associated with financial risk taking in men. Evolution and Human Behavior, vol 20:2, p. 85-92.http://www.sciencedirect.com/science/article/pii/S1090513808001165

Haradon, Z., & Galdzicki, M. (2015). DRD4 Repeats. Retrieved from http://hivebio.org/projects/ drd4-repeats/

Lichter, J. B., Barr, C. L., Kennedy, J. L., Tol, H. H. M. V., Kidd, K. K., & Livak, K. J. (1993). A hypervariable segment in the human dopamine receptor D4 (DRD4) gene. Human Molecular Genetics, 2(6), 767–773. http://doi.org/10.1093/hmg/2.6.767

Sander, T., Harms, H., Dufeu, P., Kuhn, S., Rommelspacher, H., & Schmidt, L. G. (1997). Dopamine D4 receptor exon III alleles and variation of novelty seeking in alcoholics. American Journal of Medical Genetics, 74(5), 483–487.