DRD4 promoter SNPs and gender effects on Extraversion in African Americans. 
There is strong evidence for genetic influences on personality traits.  Interest in one such gene, the dopamine D4 receptor (DRD4) grew after an exon III polymorphism was associated with Novelty Seeking and related measures of Extraversion.  However, the findings were not confirmed in later studies.  Recently, a -521C/T single nucleotide polymorphism (SNP) within the promoter region of the DRD4 gene was found to be related to Novelty Seeking scores in populations from Japan and Hungary.  Since little is known about the role DRD4 plays in personality in other populations we evaluated if two DRD4 promoter SNPs, -521C/T and -616C/G, were related to personality traits in African Americans.  Personality traits were measured by the NEO-FFI in 71 unrelated African Americans.  Genotyping was performed using PCR-RFLP.  Multivariate analyses of variance (MANOVA) were performed to evaluate the effects of gender and -616 and -521 genotypes on personality traits.  A significant three-way interaction effect from gender, -616 genotype, and -521 genotype was observed for Extraversion scores (F(1,54) 5.86, P < 0.02).  Subsequent analyses revealed that the association was mainly due to -521C/T genotype among females (P = 0.01).  This study provides further evidence that genetic variation within the DRD4 promoter and gender differences contribute to variation in Novelty Seeking behaviors such as Extraversion.