Polymorphisms in dopamine system genes are associated with individual differences in attention in infancy

Abstract

Knowledge about the functional status of the frontal cortex in infancy is limited. This study investigated the effects of polymorphisms in four dopamine system genes on performance in a task developed to assess such functioning, the Freeze-Frame task, at 9 months of age. Polymorphisms in the catechol-O-methyltransferase (COMT) and the dopamine D4 receptor (DRD4) genes are likely to impact directly on the functioning of the frontal cortex, whereas polymorphisms in the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes might influence frontal cortex functioning indirectly via strong frontostriatal connections. A significant effect of the COMT valine(1)methionine (Val 158 Met) polymorphism was found. Infants with the Met/Met genotype were significantly less distractible than infants with the Val/Val genotype in Freeze-Frame trials presenting an engaging central stimulus. In addition, there was an interaction with the DAT1 3; variable number of tandem repeats polymorphism; the COMT effect was present only in infants who did not have two copies of the DAT1 10-repeat allele. These findings indicate that dopaminergic polymorphisms affect selective aspects of attention as early as infancy and further validate the Freeze-Frame task as a frontal cortex task.

Figure 1

The effect of the catechol-O-methyltransferase (COMT) valine¹⁵⁸methionine (Val¹⁵⁸Met) and dopamine transporter (DAT1)3′ variable number of tandem repeats (VNTR) polymorphisms on Freeze-Frame performance. Error bars indicate the 95% confidence interval of the mean. (a) The mean proportion of looks to the distractors in the boring and interesting Freeze-Frame trials in the three COMT Val¹⁵⁸Met genotype groups in the Caucasian subsample (Met/Met, n = 19; Val/Met, n = 37; Val/Val, n = 23). An asterisk indicates a significant difference from the Met/Met group at p < .01. (b) The mean proportion of looks to the distractors in the boring and interesting Freeze-Frame trials in the DAT1 3′ VNTR 10/10 and non-10/10 genotype groups (10/10, n = 60; non-10/10, n = 42); the overall difference between the two genotype groups (across trial types) was significant at p < .05. (c) The effect of the COMT Val¹⁵⁸Met polymorphism on the mean proportion of looks to the distractors in the interesting Freeze-Frame trials in the two DAT1 genotype groups (10/10 + Met/Met, n = 19; 10/10 + Val/Met, n = 26; 10/10 + Val/Val, n = 15; non-10/10 + Met/Met, n = 9; non-10/10 + Val/Met, n = 21; non-10/10 + Val/Val, n = 12). An asterisk indicates a significant difference from the Met/Met group at p < .01 within the non-10/10 group, and a triangle indicates a significant difference at p < .01 between the Val/Met group in the non-10/10 group compared with the Val/Met group in the 10/10 group.