Abstract
BackgroundResearch on the genetic basis for impulsivity has revealed an array of ambiguous findings. This may be a result of limitations to self-report assessments of impulsivity. Behavioral measures that assess more narrowly defined aspects of impulsivity may clarify genetic influences. This study examined the relationship between possession of the DRD2 TaqI A and DRD4 48 bp VNTR genetic polymorphisms and performance on a behavioral measure of impulsivity, the delay discounting task (DDT), and three traditional self-report measures.Methods195 individuals (42% male) were recruited from a university campus and were assessed in small group sessions using personal computers. Genotyping was conducted using previously established protocols. For the DRD2 TaqI A locus, individuals were designated as possessing at least one copy of the A1 allele (A1+) or not (A1-), and for the DRD4 48-bp VNTR locus, individuals were designated as having at least one long allele (7 repeats or longer, L+) or not (L-). Principal analyses used multiple univariate factorial 2 (A1+/A1-) × 2 (L+/L-) analyses of variance.ResultsA significant main effect of A1+ status on DDT performance was evident (p = .006) as well as a significant interaction effect (p = .006) between both genes. No other significant effects were evident on the self-report measures, with the exception of a trend toward an interaction effect on the Sensation Seeking Scale. Exploratory analyses suggested that the significant effects were not a function of population stratification or gender.DiscussionThese data suggest that the DRD2 TaqI A and DRD4 VNTR polymorphisms influence impulsivity as measured with a delay discounting task. Specifically, these findings suggest that an interaction between the functional effects of the two unlinked genotypes results in significant difference in the balance of mesolimbic dopaminergic activation relative to frontal-parietal activation. However, these findings are also the first in this area and must be replicated.ConclusionThese findings suggest a meaningful interaction between the DRD2 TaqI A and DRD4 VNTR polymorphisms in the expression of impulsivity and provide initial support for the utility of using behavioral measures for clarifying genetic influences on impulsivity.
Highlights
Research on the genetic basis for impulsivity has revealed an array of ambiguous findings
The two dopaminergic genetic polymorphisms we examined were the DRD2 TaqI A and DRD4 48 bp Variable Number of Tandem Repeats (VNTR) polymorphisms
We found no evidence of population stratification, studies of delay discounting as a potential endophenotype in larger samples of non-European descendants will be important to address the generalizability of these findings
Summary
Research on the genetic basis for impulsivity has revealed an array of ambiguous findings. Impulsivity is a prototypic candidate for the endophenotype approach because it is a trait that varies considerably in the overall population [9,10,11,12] and is associated with an array of psychiatric disorders. These include alcohol and drug dependence [13,14,15,16,17,18,19], pathological gambling [20,21], attention deficit-hyperactivity disorder (ADHD) [22,23], borderline personality disorder [24] and antisocial personality disorder [25,26,27]. The relative contributions of genetic and environmental variables are unclear at this point, converging lines of evidence suggest genetic factors play an important role
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