Influence of the OPRM1 gene polymorphism upon children's degree of withdrawal and brain activation in response to facial expressions.

Genetic variation of the A118G polymorphism of the μ-opioid receptor gene (OPRM1) predicts individual sensitivity to social rejection and fMRI activation during simulated social rejection in adults, while data on these relationships during childhood are lacking. We investigated whether this polymorphism predicts childhood withdrawal - a predictor of sensitivity to social rejection -, and the face-specific N170 event-related waveform in response to facial expressions. Among facial expressions, 'anger' was expected to be particularly evocative, as it communicates social rejection. Forty-nine children aged 8-10 years were characterised for their OPRM1 genotype, their score at the Withdrawn Scale of the Child Behavior Checklist (CBCL), and for N170 latencies and amplitudes recorded during a task of implicit processing of happy, neutral, and angry expressions of other children. Children carrying the OPRM1-G allele had higher CBCL Withdrawn scores and enhanced N170 amplitudes in response to facial expressions. Multiple linear regressions showed that the Withdrawn scale score predicts larger N170 amplitudes at the Pz and C4 electrodes, only for the anger expression. Children who carry one or two copies of the OPRM1 G-allele are more likely to manifest withdrawn behaviours, and differ for electrophysiological responses to the early phases of processing affective stimuli.