Extraversion. Interaction between D2 dopamine receptor polymorphisms and parental alcoholism.

Both molecular genetic factors (the D2 dopamine receptor (DRD2) and the D4 dopamine receptor (DRD4) polymorphisms) and environmental influences of living in an alcoholic or nonalcoholic home on the personality traits of Extraversion and Neuroticism were assessed in drug-naive, young adolescent boys. There were no significant main effects of genetic or environmental factors on either Neuroticism or Extraversion as measured by the Junior Eysenck Personality Inventory (JEPI). However, a significant interaction between DRD2 (but not DRD4) alleles and environmental variables was observed on Extraversion. Specifically, children with the minor alleles of the DRD2 gene showed a significantly greater Extraversion score when living in an alcoholic than in a nonalcoholic home. In contrast, children with the major alleles of the DRD2 gene showed a trend in the opposite direction. Although the results are preliminary and pending replication, they nevertheless provide the first report of a specific gene-environment interaction involving a human personality trait.