Taken together, acknowledging the relatively small number of studies and ambiguities to date, the assembled findings nonetheless ‘tick-the-boxes’ for delay discounting as an endophenotype. There is evidence that delay discounting decision-making is a stable and heritable phenotype; that elevations in impulsive discounting are present in otherwise unaffected individuals who are FH+ for addictive disorders; and that specific forms of genetic variation are associated with significant differences in discounting preferences. These findings thus provide the critical second link, that genetic factors are partially responsible for discounting decision-making. Moreover, in the case of strain-based differences in discounting, there is also evidence that differences aggregate with strains that also engage in more addictive behavior. This connection has not been made directly in humans, however, and while the findings to date suggest this is a highly promising prospect, it is by no means established or a foregone conclusion. Future progress will depend on further articulating the links between genetic factors, discounting preferences, and risk for developing an addictive disorder.
