Dopamine D4 receptor (D4DR) and serotonin transporter promoter (5-HTTLPR) polymorphisms in the determination of temperament in 2-month-old infants

We have previously shown that the dopamine D4 exon III repeat (D4DR) and the sertonin transporter promoter region (5-HTTLPR) polymosphisms are not only associated with adult personality traits but also partially determine temperament in 2-week old neonates. We now report the results of a second study of these neonates and their behavioral assessment at 2 months using Rothbart's Infant Behavioral Questionnaire (IBQ). Negative correlations were observed between one IBQ behavioral cluster, Distress to Limitations, that measures an infant's response to stressful conditions, and all four core temperaments assessed by the Neonatal Behavioral Assessment Scale (NBAS) that we employed at 2 weeks (Orientation, r = -0.3; Motor Organization, r = -0.34; Range of State, r = -0.24; and Regulation of State, r = -0.179). Significant main effects were observed when Distress to Limitations scores for these infants were grouped by the D4DR and 5-HTTLPR polymorphisms (two-way ANOVA: F_D4DR = 8.45, P = 0.005 and F_5-HTTLPR = 5.90, P = 0.018). Distress to Limitations, a temperament perhaps akin to adult Neuroticism, is influenced by both the D4DR and 5-HTTLPR polymorphisms. In these infants, the expression of the short serotonin promoter region polymorphism (linked in some adult studies to Neuroticism) on raising Distress to Limitations scores is only apparent in infants lacking the long D4DR exon III repeat alleles (linked in some adult studies to Novelty Seeking). This correlation between behavioral clusters assessed at 2 weeks and at 2 months appears to be partially based on the interaction between two common polymorphisms, 5-HTTLPR and D4DR that jointly contribute to the partial determination of these temperaments.