Genome-wide association and genetic functional studies identify autism susceptibility candidate 2 gene (AUTS2) in the regulation of alcohol consumption

Abstract

Alcohol consumption is a moderately heritable trait, but the genetic basis in humans is largely unknown, despite its clinical and societal importance. We report a genome-wide association study meta-analysis of ∼2.5 million directly genotyped or imputed SNPs with alcohol consumption (gram per day per kilogram body weight) among 12 population-based samples of European ancestry, comprising 26,316 individuals, with replication genotyping in an additional 21,185 individuals. SNP rs6943555 in autism susceptibility candidate 2 gene (AUTS2) was associated with alcohol consumption at genome-wide significance (P = 4 × 10(-8) to P = 4 × 10(-9)). We found a genotype-specific expression of AUTS2 in 96 human prefrontal cortex samples (P = 0.026) and significant (P < 0.017) differences in expression of AUTS2 in whole-brain extracts of mice selected for differences in voluntary alcohol consumption. Down-regulation of an AUTS2 homolog caused reduced alcohol sensitivity in Drosophila (P < 0.001). Our finding of a regulator of alcohol consumption adds knowledge to our understanding of genetic mechanisms influencing alcohol drinking behavior.

Fig. 1.

Functional genetic analysis of AUTS2. (A) Tissue-specific quantitative mRNA expression. Mean mRNA level (SE) of AUTS2, represented by 100/δ Ct, across three independent experiments in human amygdala, frontal cortex, putamen, and liver. Mean Ct values for the housekeeping gene (GAPDH) were similar across tissues: 21.97, 22.42, 21.64, and 19.93, respectively. (B) Genotype-specific quantitative mRNA expression in human prefrontal cortex. Generalized linear model for AUTS2 mRNA levels. Increased AUTS2 mRNA expression observed in carriers of the minor A allele of rs6943555 relative to the major T allele; gene dose effect was significant at P = 0.026. Regression estimates and SEs are shown for the predictors in the model; negative normalized ΔCt values indicate higher expression levels. (C) Line diagram representing tay (dAUTS2) gene region of Drosophila melanogaster. Exons are shown as boxes and positions of P-element insertions by vertical arrows. Direction of transcription is to the right (arrow; http://flybase.org). (D and E) Sensitivity to ethanol sedation of flies with dAUTS2/tay P-element insertion. P-element insertion mutants KG00195 and NP0941, in the 5′-UTR and first intron of tay, respectively, exhibit strongly reduced sensitivity to ethanol sedation relative to the control strain (F_2,23 = 20.7; ***P < 0.001; n = 8). (F and G) Sensitivity to ethanol sedation of flies expressing dAUTS2/tay RNAi in neurons. Flies harboring both the neuronal GAL4 driver elav-GAL4^c155 and the Gal4-responsive UAS-tay^RNAi construct exhibited significantly reduced sensitivity to ethanol sedation compared with control flies harboring either transgene alone (F_2,23 = 7.4; **P = 0.004; n = 8). (H and I) Ethanol absorption of flies with reduced dAUTS2/tay. Internal ethanol concentrations after ethanol exposure for (H) tay RNAi experiment and (I) tay mutants. Neuronal expression of dAUTS2 RNAi did not alter ethanol absorption (F_2,23 = 2.55; P = 0.1; n = 8), and mutants in dAUTS2/tay did not show any significant difference from controls (F_2,11 = 0.252; P = 0.78; n = 4).