title: Genetic basis of delay discounting in frequent gamblers: examination of a priori candidates and exploration of a panel of dopamine-related loci.
abstract: BACKGROUND
  Delay discounting is a behavioral economic index of impulsivity that reflects preferences for small immediate rewards relative to larger delayed rewards. It has been consistently linked to pathological gambling and other forms of addictive behavior, and has been proposed to be a behavioral characteristic that may link genetic variation and risk of developing addictive disorders (i.e., an endophenotype). Studies to date have revealed significant associations with polymorphisms associated with dopamine neurotransmission. The current study examined associations between delay discounting and both previously linked variants and a novel panel of dopamine-related variants in a sample of frequent gamblers.
  
  
  METHODS
  Participants were 175 weekly gamblers of European ancestry who completed the Monetary Choice Questionnaire to assess delay discounting preferences and provided a DNA via saliva.
  
  
  RESULTS
  In a priori tests, two loci previously associated with delayed reward discounting (rs1800497 and rs4680) were not replicated, however, the long form of DRD4 VNTR was significantly associated with lower discounting of delayed rewards. Exploratory analysis of the dopamine-related panel revealed 11 additional significant associations in genes associated with dopamine synthesis, breakdown, reuptake, and receptor function (DRD3, SLC6A3, DDC, DBH, and SLC18A2). An aggregate genetic risk score from the nominally significant loci accounted for 17% of the variance in discounting. Mediational analyses largely supported the presence of indirect effects between the associated loci, delay discounting, and pathological gambling severity.
  
  
  CONCLUSIONS
  These findings do not replicate previously reported associations but identify several novel candidates and provide preliminary support for a systems biology approach to understand the genetic basis of delay discounting.
authors.affiliation: Department of Psychology, University of Georgia Athens, Georgia.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Gray
authors.affiliation: Boris Centre for Addictions Research, Department of Psychiatry and Behavioural Neurosciences, McMaster University Hamilton, Ontario, Canada.
authors.forename: James
authors.initials: J
authors.lastname: MacKillop
mesh_terms: D065786:Delay Discounting; D004298:Dopamine; D005715:Gambling / Q000235:genetics*; D056726:Genetic Association Studies; D060005:Genotyping Techniques; D006801:Humans; D007175:Impulsive Behavior; D057566:Self Report; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D044465:White People / Q000235:genetics
chemical_list: D004298:Dopamine
keywords: Delay discounting; dopamine; endophenotype; genetics; impulsivity; pathological gambling