Genetic approaches to addiction: genes and alcohol

Abstract

Aims: Alcoholism is a chronic relapsing disorder with an enormous societal impact. Understanding the genetic basis of alcoholism is crucial to characterize individuals' risk and to develop efficacious prevention and treatment strategies.

Methods: We examined the available scientific literature to provide an overview of different approaches that are being integrated increasingly to advance our knowledge of the genetic bases of alcoholism. Examples of genes that have been shown to influence vulnerability to alcoholism and related phenotypes are also discussed.

Results: Genetic factors account for more than 50% of the variance in alcoholism liability. Susceptibility loci for alcoholism include both alcohol-specific genes acting either at the pharmacokinetic or pharmacodynamic levels, as well as loci moderating neuronal pathways such as reward, behavioral control and stress resiliency, that are involved in several psychiatric diseases. In recent years, major progress in gene identification has occurred using intermediate phenotypes such as task-related brain activation that confer the advantage of increased power and the opportunity of exploring the neuronal mechanisms through which genetic variation is translated into behavior. Fundamental to the detection of gene effects is also the understanding of the interplay between genes as well as genes/environment interactions. Whole Genome Association studies represent a unique opportunity to identify alcohol-related loci in hypothesis-free fashion. Finally, genome-wide analyses of transcripts and chromatin remodeling promise an increase in our understanding of the genome function and of the mechanisms through which gene and environment cause diseases.

Conclusions: Although the genetic bases of alcoholism remain largely unknown, there are reasons to think that more genes will be discovered in the future. Multiple and complementary approaches will be required to piece together the mosaic of causation.

Figure 1

Catechol-O-methyltransferase (COMT): the warrior (Val158) versus worrier (Met158) model

Figure 2

Main and interactive effects of genetic and environmental risk factors for alcoholism

Figure 3

Genotype-specific effect size (odds ratios) for complex versus intermediate phenotypes. CAD = coronary artery disease; T1D = Type 1 diabetes; T2D = Type 2 diabetes; CD = Crohn's disease; BP = bipolar disorder; RA = rheumatoid arthritis; HA = harm avoidance; MAOA = monoamine oxidase A; HTT = serotonin transporter; LPR = linked polymorphic region; COMT = catechol-O-methyltransferase