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

Abstract

We and others have previously shown that the dopamine D4 exon III repeat (D4DR) and the serotonin-transporter promoter region (5-HTTLPR) polymorphisms are not only associated with adult personality traits^1–7 but also with temperament in 2-week-old neonates.⁸ We now report the results of a second study of these infants and their temperament at 2 months using Rothbart's Infant Behavior Questionnaire (IBQ).⁹ There were significant negative correlations between neonatal orientation and motor organization as measured by the Neonatal Behavioral Assessment Scale (NBAS)¹⁰ at 2 weeks and negative emotionality, especially distress in daily situations, at 2 months of age. There were significant main effects for negative emotionality and distress when the infants were grouped by the D4DR and the 5-HTTLPR polymorphisms. Infants with long D4DR alleles had significantly lower scores on Negative Emotionality (F[1,72] = 8.50, P = 0.005) and Distress to Limitations (F[1,72] = 4.93, P = 0.03) than infants with short D4DR alleles. In contrast, infants with the short homozygous (s/s) 5-HTTLPR genotype had higher scores on Negative Emotionality (F[1,72] = 3.88, P = 0.053) and Distress to Limitations (F[1,72] = 4.94, P = 0.029) than infants with the I/s or I/I genotypes. The strongest effects occurred in those infants with the s/s 5-HTTLPR polymorphism who also were lacking long D4DR alleles which in some studies has been linked to adult novelty seeking.^1,6 These infants showed most negative emotionality and most distress to daily situations, temperament traits that are perhaps the underpinning of adult neuroticism.