Liability to alcohol dependence (AD) is heritable, but little is known about its complex polygenic architecture or its genetic relationship with other disorders. To discover loci associated with AD and characterize the relationship between AD and other psychiatric and behavioral outcomes, we carried out the largest GWAS to date of DSM-IV diagnosed AD. Genome-wide data on 14,904 individuals with AD and 37,944 controls from 28 case/control and family-based studies were meta-analyzed, stratified by genetic ancestry (European, N = 46,568; African; N = 6,280). Independent, genome-wide significant effects of different ADH1B variants were identified in European (rs1229984; p = 9.8E-13) and African ancestries (rs2066702; p = 2.2E-9). Significant genetic correlations were observed with 17 phenotypes, including schizophrenia, ADHD, depression, and use of cigarettes and cannabis. The genetic underpinnings of AD only partially overlap with those for alcohol consumption, underscoring the genetic distinction between pathological and non-pathological drinking behaviors.

Genome-wide association studies (GWASs) have focused primarily on populations of European descent, but it is essential that diverse populations become better represented. Increasing diversity among study participants will advance our understanding of genetic architecture in all populations and ensure that genetic research is broadly applicable. To facilitate and promote research in multiancestry and admixed cohorts, we outline key methodological considerations and highlight opportunities, challenges, solutions, and areas in need of development. Despite the perception that analyzing genetic data from diverse populations is difficult, it is scientifically and ethically imperative, and there is an expanding analytical toolbox to do it well.

Aggressive behavior is important for animal survival and reproduction, and excessive aggression is an enormous social and economic burden for human society. Although the role of biogenic amines in modulating aggressive behavior is well characterized, other genetic mechanisms affecting this complex behavior remain elusive. Here, we developed an assay to rapidly quantify aggressive behavior in Drosophila melanogaster, and generated replicate selection lines with divergent levels of aggression. The realized heritability of aggressive behavior was approximately 0.10, and the phenotypic response to selection specifically affected aggression. We used whole-genome expression analysis to identify 1,539 probe sets with different expression levels between the selection lines when pooled across replicates, at a false discovery rate of 0.001. We quantified the aggressive behavior of 19 mutations in candidate genes that were generated in a common co-isogenic background, and identified 15 novel genes affecting aggressive behavior. Expression profiling of genetically divergent lines is an effective strategy for identifying genes affecting complex traits.

Finding genes involved in complex behavioral outcomes, and understanding the pathways by which they confer risk, is a challenging task, necessitating large samples that are phenotypically well characterized across time. We describe an effort to create a university-wide research project aimed at understanding how genes and environments impact alcohol use and related substance use and mental health outcomes across time in college students. Nearly 70% of the incoming freshman class (N = 2715) completed on-line surveys, with 80% of the students from the fall completing spring follow-ups. 98% of eligible participants also gave DNA. The participants closely approximated the university population in terms of gender and racial/ethnic composition. Here we provide initial results on alcohol use outcomes from the first wave of the sample, as well as associated predictor variables. We discuss the potential for this kind of research to advance our understanding of genetic and environment influences on substance use and mental health outcomes.

IMPORTANCE Alcohol use disorder (AUD) runs strongly in families. It is unclear to what extent the cross-generational transmission of AUD results from genetic vs environmental factors. OBJECTIVE To determine to what extent genetic and environmental factors contribute to the risk for AUD.DESIGN, SETTING, AND PARTICIPANTS Follow-up in 8 public data registers of adoptees, their biological and adoptive relatives, and offspring and parents from stepfamilies and not-lived-with families in Sweden. In this cohort study, subtypes of AUD were assessed by latent class analysis. A total of 18 115 adoptees (born 1950-1993) and 171 989 and 107 696 offspring of not-lived-with parents and stepparents, respectively (born 1960-1993).MAIN OUTCOMES AND MEASURES Alcohol use disorder recorded in medical, legal, or pharmacy registry records.RESULTS Alcohol use disorder in adoptees was significantly predicted by AUD in biological parents (odds ratio, 1.46; 95% CI, 1.29-1.66) and siblings (odds ratio, 1.94; 95% CI, 1.55-2.44) as well as adoptive parents (odds ratio, 1.40; 95% CI, 1.09-1.80). Genetic and environmental risk indices created from biological and adoptive relatives acted additively on adoptee AUD liability. Results from biological and adoptive relatives were replicated and extended from examinations of, respectively, not-lived-with parents and stepparents. Multivariate models in these families showed that AUD in offspring was significantly predicted by AUD, drug abuse, psychiatric illness, and crime in not-lived-with parents and by AUD, drug abuse, crime, and premature death in stepparents. Latent class analyses of adoptees and offspring of not-lived-with parents with AUDs revealed 3 AUD classes characterized by (1) female preponderance and high rates of psychiatric illness, (2) mild nonrecurrent symptoms, and (3) early-onset recurrence, drug abuse, and crime. These classes had distinct genetic signatures in the patterns of risk for various disorders in their not-lived-with parents and striking differences in the rates of recorded mood disorders.CONCLUSIONS AND RELEVANCE Parent-offspring transmission of AUD results from both genetic and environmental factors. Genetic risk for AUD reflects both a specific liability to AUD and to other externalizing disorders. Environmental risk reflects features of both parental psychopathology and other aspects of the rearing environment. Alcohol use disorder is a heterogeneous syndrome and meaningful subtypes emerged from latent class analysis, which were validated by patterns of disorders in biological parents and specific psychiatric comorbidities. The general population contains informative family constellations that can complement more traditional adoption designs in clarifying the sources of parent-offspring resemblance.