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Monday, April 23, 2012

Impulsiveness and insula activation during reward anticipation are associated with genetic variants in GABRA2 in a family sample enriched for alcoholi

Genetic factors, externalizing personality traits such as impulsivity, and brain processing of salient stimuli all can affect individual risk for alcoholism.

One of very few confirmed genetic association findings differentiating alcoholics from non-alcoholics is with variants in the inhibitory γ-amino butyric acid α2 receptor subunit (GABRA2) gene.

Here we report the association of two of these GABRA2 variants with measures of alcohol symptoms, impulsivity and with insula cortex activation during anticipation of reward or loss using functional magnetic resonance imaging (fMRI).

In a sample of 173 families (449 subjects), 129 of whom had at least one member diagnosed with alcohol dependence or abuse, carriers for the G allele in two single-nucleotide polymorphisms (SNPs) and haplotypes were more likely to have alcohol dependence symptoms (rs279858, P=0.01; rs279826, P=0.05; haplotype, P=0.02) and higher NEO Personality Inventory-Revised (NEO-PI-R) Impulsiveness scores (rs279858, P=0.016; rs279826, P=0.012; haplotype, P=0.032) with a stronger effect in women (rs279858, P=0.011; rs279826, P=0.002; haplotype, P=0.006), all P-values are corrected for family history and age.

A subset of offspring from these families (n=44, 20 females), genotyped for GABRA2, participated in an fMRI study using a monetary incentive delay task.

Increased insula activation during reward (r2=0.4; P=0.026) and loss (r2=0.38; P=0.039) anticipation was correlated with NEO-PI-R Impulsiveness and further associated with the GG genotype for both SNPs (P's<0.04).

Our results suggest that GABRA2 genetic variation is associated with Impulsiveness through variation of insula activity responses, here evidenced during anticipatory responses.

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