Genetic differences in response to alcohol

FACTORS CONTRIBUTING TO THE ESCALATION OF ALCOHOL CONSUMPTION

Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.

Convergent Evidence From Humans and Drosophila melanogaster Implicates the Transcription Factor MEF2B/Mef2 in Alcohol Sensitivity

BACKGROUND

Self-Rating of the Effects of Alcohol (SRE) measures level of response to ethanol (EtOH) in humans. Interestingly, there is a positive relationship between the SRE and risk for abusing alcohol, suggesting mechanistic connections between SRE and alcohol abuse.

METHODS

To identify candidate genes with a role in SRE and alcohol-related behavior more generally, we coupled human genetic analyses with studies in Drosophila melanogaster. We first performed a gene-based analysis of Genomewide association studies (GWAS) summary statistics for SRE in the Avon Longitudinal Study of Parents and Children sample. Based on prior findings in humans, orthology to fly genes, and the availability of genetic reagents, we selected a subset of these genes for studies on EtOH behavior in Drosophila.

RESULTS

We found 37 genes with nominal associations in our SRE GWAS. We explored the role of 6 orthologous genes in Drosophila EtOH sedation and rapid tolerance. We found that the transcription factor Mef2 is required for normal EtOH sedation in flies. Pan-neuronal expression of 2 independent Mef2 RNAi transgenes significantly reduced Mef2 expression and made flies resistant to EtOH sedation. Additionally, flies with multiple independent mutant alleles of Mef2 were also resistant to EtOH sedation, confirming a role for Mef2 in this behavior. Altered expression of Mef2 did not change EtOH rapid tolerance or cause a net change in internal EtOH concentrations.

CONCLUSIONS

Our studies indicate that MEF2B influences SRE in humans and that Mef2 impacts EtOH sedation in Drosophila.

Missense Gamma-Aminobutyric Acid Receptor Polymorphisms Are Associated with Reaction Time, Motor Time, and Ethanol Effects in Vivo

Background: The Gamma-aminobutyric acid type A receptor (GABA-A receptor) is affected by ethanol concentrations equivalent to those reached during social drinking. At these concentrations, ethanol usually causes impairment in reaction and motor times in most, but not all, individuals.

Objectives: To study the effect of GABA-A receptor variability in motor and reaction times, and the effect of low ethanol doses.

Methods: Two hundred and fifty healthy subjects received one single dose of 0.5 g/Kg ethanol per os. Reaction and motor times were determined before ethanol challenge (basal), and when participants reached peak ethanol concentrations. We analyzed all common missense polymorphisms described in the 19 genes coding for the GABA-A receptor subunits by using TaqMan probes.

Results: The GABRA6 rs4454083 T/C polymorphisms were related to motor times, with individuals carrying the C/C genotype having faster motor times, both, at basal and at peak ethanol concentrations. The GABRA4 rs2229940 T/T genotype was associated to faster reaction times and with lower ethanol effects, determined as the difference between basal reaction time and reaction time at peak concentrations. All these associations remained significant after correction for multiple comparisons. No significant associations were observed for the common missense SNPs GABRB3 rs12910925, GABRG2 rs211035, GABRE rs1139916, GABRP rs1063310, GABRQ rs3810651, GABRR1 rs12200969 or rs1186902, GABRR2 rs282129, and GABRR3 rs832032.

Conclusions: This study provides novel information supporting a role of missense GABA-A receptor polymorphisms in reaction time, motor time and effects of low ethanol doses in vivo.

Subjective Response to Alcohol as a Research Domain Criterion

BACKGROUND

Individual differences in the subjective experience of the pharmacological effects of alcohol have long been implicated in the likelihood that one will drink heavily and develop alcoholism. The theme of this conceptual review and perspective article is to synthesize the literature on subjective responses to alcohol and to set an agenda for the next generation of research in the area. Specifically, we contend that in order for subjective response to alcohol to play a prominent role in alcoholism research, it is critical that it be studied as a multimodal phenotype.

METHODS

First, we review the human research on subjective response to alcohol measured under controlled laboratory conditions and draw recommendations for the application of these findings to understanding alcoholism neurobiology in humans. Second, we highlight multimodal approaches, including studies of the genetic and neural substrates of individual differences in subjective response to alcohol. Third, we review treatment implications with a focus on subjective response to alcohol as an intervention target. Upon review of the research on subjective response to alcohol across levels of analyses, we provide recommendations for leveraging these phenotypes in a systematic and methodologically rigorous fashion that can address central questions about alcoholism etiology, disease progression, and personalized treatment.

DISCUSSION

The approach recommended herein is largely consistent with the Research Domain Criteria (RDoC) initiative across the National Institute of Mental Health. The defining feature of such domains is that they inform behavior yet be amenable to examination through multiple units of analysis, such as molecular, genetic, circuit-level, and behavioral measurements. To that end, we contend that subjective response to alcohol represents a behaviorally and biologically plausible phenotype upon which to build using the RDoC framework for understanding alcohol use disorder.