Ishii et al. (2017)

Ishii, K. (石井敬子), Matsunaga, M., Noguchi, Y., Yamasue, H. Ochi, M. (越智美早), & Ohtsubo, Y. (大坪庸介) (2017) . 
A polymorphism of serotonin 2A receptor (5-HT2AR) influences delay discounting. 
Personality and Individual Differences. 
doi: 10.1016/j.paid.2017.03.011
The present study investigated the association between a polymorphism of the serotonin 2A receptor (5-HT2AR) gene and the form of impulsive choice known as delay discounting. Using a hypothetical situation, we asked Japanese participants to choose between receiving (or paying) a different amount of money immediately or with a specified delay (one week, two weeks, one month, six months, one year, five years, or 25 years), and estimated the parameters of intertemporal choice models (exponential, hyperbolic, hyperbolic with exponent, and quasi-hyperbolic). Regardless of the genotypes, the hyperbolic with exponent model, which always indicated minimum AICc (Akaike Information Criterion with small sample correction), fitted better the observed data than the other models. Future gains were discounted more steeply than future losses. Moreover, as expected, individuals with the AA genotype of the 5-HT2AR A-1438G polymorphism discounted the future more steeply than did individuals with the GG genotype, although this effect was limited to only gains. The findings implied individual differences based on the A-1438G polymorphism in the modulation of serotonin in the reward valuation underlying delay discounting.