While many twin studies have examined disorder status as a phenotype, only one twin study has assessed discounting. Anokhin et al. (2011) examined the heritability of delay discounting in early adolescent twins who were assessed using a single item discounting measure at age 12 and 14 and found evidence for additive genetic influences at both ages (age 12, a2 = .30; age 14, a2 = .51). Interestingly, however, the best fitting model indicated significant genetic influences at age 12 predicting discounting at both age 12 and 14, but also with significant non-shared environmental influences at both ages 12 and 14. In other words, these results suggest that discounting is indeed a heritable phenotype but both genetic and environmental influences appear to be operative.
