Disentangling Social-Genetic From Rearing-Environment Effects for Alcohol Use Disorder Using Swedish National Data

Peer Social Genetic Effects and the Etiology of Substance Use Disorders, Major Depression, and Anxiety Disorder in a Swedish National Sample

OBJECTIVE

There is growing interest in how peers' genotypes may influence health (i.e., peer social genetic effects). The authors sought to clarify the nature of peer social genetic effects on risk for drug use disorder, alcohol use disorder (AUD), major depression, and anxiety disorder.

METHOD

Cox models were used with data from a population-based Swedish cohort (N=655,327). Outcomes were drug use disorder, AUD, major depression, and anxiety disorder registrations between ages 17 and 30 from medical, criminal, and pharmacy registries. The authors indexed peer social genetic effects with peers' family genetic risk scores (FGRSs) for the same disorders, which are personalized measures of genetic risk inferred from diagnoses in first- to fifth-degree relatives.

RESULTS

Across disorders, peer FGRSs predicted increased risks of proband registration (hazard ratio range, 1.01-1.59), with stronger effects for drug use disorder and AUD than for major depression and anxiety disorder. Peer social genetic effects were stronger for school classmates than for geographically proximal peers, and for peers from upper secondary school (ages 16-19) versus peers from lower secondary school (ages 7-16). Peer social genetic effects remained significant following statistical control for sociodemographic confounders, whether peers were affected, and peers' FGRS for educational attainment. Peer social genetic effects were more pronounced for probands at higher genetic risk.

CONCLUSIONS

The genetic makeup of adolescents' peers has long-reaching consequences on risks for drug use disorder, AUD, major depression, and anxiety disorder. Individuals at high genetic risk are more sensitive to social genetic effects. Alternative hypotheses such as sociodemographic stratification, exposure to affected peers, and genetic predispositions for educational attainment did not explain the risk associated with peer social genetic effects for substance use and psychiatric disorders.

Partners in Health: Investigating Social Genetic Effects Among Married and Cohabiting Couples

Partners resemble each other in health behaviors and outcomes such as alcohol use, smoking, physical activity, and obesity. While this is consistent with social contagion theory suggesting partner influence, it is notoriously difficult to establish causality because of assortative mating and contextual confounding. We offer a novel approach to studying social contagion in health in long-term partnerships by combining genetic data of both partners in married/cohabiting couples with longitudinal data on their health behaviors and outcomes. We examine the influence of the partner's genetic predisposition for three health outcomes and behaviors (BMI, smoking, and drinking) among married/cohabiting couples. We use longitudinal data from the Health and Retirement Study and the English Longitudinal Study of Ageing with data on health outcomes and genotypes for both partners. Results show that changes over time in BMI, smoking, and drinking depend on the partner's genetic predispositions to these traits. These findings underline the importance of people's social surroundings for their health and highlight the potential of targeting health interventions at couples.

Genetic and Cultural Transmission of Alcohol Use Disorder in Swedish Twin Pedigrees

OBJECTIVE

Using Swedish nationwide registry data, we investigated the contribution of genetic and environmental risk factors to the etiology of alcohol use disorder (AUD) by extended twin pedigree modeling.

METHOD

AUD was defined using public inpatient, outpatient, prescription, and criminal records. Three-generational pedigrees were selected for index individuals born between 1980 and 1990, obtained from the national twin and genealogical registers, whose parents were twins. Relatives of the twins included in the pedigrees were their parents, siblings, spouses, and children. Genetic structural equation modeling was applied to the population-based data on AUD, using OpenMx, with age used as a covariate.

RESULTS

Analyses including up to 162,469 individuals in 18,971 pedigrees estimated AUD prevalence at 5%-12% in men and 2%-5% in women. Results indicated substantial heritability (about 50%-60%), of which a portion upwards of 5% was attributable to the consequences of assortative mating. Contributions of shared environmental factors to AUD, which represent a mix of within- and cross-generational effects, appeared to be moderate (about 10%-20%). Unique environment accounted for the remaining variance (about 20%-30%). Sex differences in the magnitude of the variance components suggested higher heritability in men and correspondingly higher shared environmental contributions in women.

CONCLUSIONS

Using objective registry data, we found that AUD is highly heritable. Furthermore, shared environmental factors contributed significantly to the liability of AUD in both men and women.

Social genetic effects for drug use disorder among spouses

AIMS

Preclinical and human studies suggest that a social partner's genotype may be associated with addiction-related outcomes. This study measured whether spousal genetic makeup is associated with risk of developing drug use disorder (DUD) during marriage and whether the risk associated with a spouse's genotype could be disentangled from potentially confounding rearing environmental effects.

DESIGN

Univariable and multivariable logistic regression analyses.

SETTING

Sweden.

PARTICIPANTS

Men and women born between 1960 and 1990 and in opposite-sex first marriages before age 35 (n = 294 748 couples).

MEASUREMENTS

Outcome was DUD diagnosis (inclusive of opioids, sedatives/hypnotics/anxiolytics, cocaine, cannabis, amphetamine and other psychostimulants, hallucinogens, other drugs of abuse and combinations thereof) obtained from legal, medical and pharmacy registries. The focal predictor was family genetic risk scores for DUD (FGRS-DUD), which were inferred from diagnoses in first- through fifth-degree relatives and weighted by degree of genetic sharing. FGRS-DUD were calculated separately for each partner in a couple.

FINDINGS

Marriage to a spouse with a high FGRS-DUD was associated with increased risk of developing DUD during marriage, OR_males  = 1.68 (95% CI = 1.50, 1.88) and OR_females  = 1.35 (1.16, 1.56), above and beyond the risk associated with one's own FGRS-DUD. The risk associated with a spouse's FGRS-DUD remained statistically significant after covarying for parental education. As indicated by a series of null interaction effects, there was no evidence that the risk associated with a spouse's FGRS-DUD differed depending on whether the spouse was DUD-affected, probands' probable contact with in-laws and whether the spouse was raised by his/her biological parents or in another home.

CONCLUSIONS

There is relatively robust evidence that a person's risk for developing drug use disorder is associated with the genetic makeup of the person's spouse.