DOPAMINE GENES AND INFANT ATTENTION 1 Polymorphisms in Dopamine System Genes are Associated with Individual Differences

1 Knowledge about the functional status of the frontal cortex in infancy is limited. This study 2 investigated the effects of polymorphisms in four dopamine system genes on performance in 3 a task developed to assess such functioning, the Freeze-Frame task, at 9 months of age. 4 Polymorphisms in the catechol-O-methyltransferase (COMT) and the dopamine D4 receptor 5 (DRD4) genes are likely to impact directly on the functioning of the frontal cortex, while 6 polymorphisms in the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) 7 genes might influence frontal cortex functioning indirectly via strong fronto-striatal 8 connections. A significant effect of the COMT ValMet polymorphism was found. Infants 9 with the Met/Met genotype were significantly less distractible than infants with the Val/Val 10 genotype in Freeze-Frame trials presenting an engaging central stimulus. In addition, there 11 was an interaction with the DAT1 3’ VNTR polymorphism; the COMT effect was only 12 present in infants who did not have two copies of the DAT1 10-repeat allele. These findings 13 indicate that dopaminergic polymorphisms already affect selective aspects of attention in 14 infancy, and further validate the Freeze-Frame task as a frontal cortex task. 15 16