Contributions of Genes and Environment to Developmental Change in Alcohol Use

A Developmentally-Informative Genome-wide Association Study of Alcohol Use Frequency

Contemporary genome-wide association study (GWAS) methods typically do not account for variability in genetic effects throughout development. We applied genomic structural equation modeling to combine developmentally-informative phenotype data and GWAS to create polygenic scores (PGS) for alcohol use frequency that are specific to developmental stage. Longitudinal cohort studies targeted for gene-identification analyses include the Collaborative Study on the Genetics of Alcoholism (adolescence n = 1,118, early adulthood n = 2,762, adulthood n = 5,255), the National Longitudinal Study of Adolescent to Adult Health (adolescence n = 3,089, early adulthood n = 3,993, adulthood n = 5,149), and the Avon Longitudinal Study of Parents and Children (ALSPAC; adolescence n = 5,382, early adulthood n = 3,613). PGS validation analyses were conducted in the COGA sample using an alternate version of the discovery analysis with COGA removed. Results suggest that genetic liability for alcohol use frequency in adolescence may be distinct from genetic liability for alcohol use frequency later in developmental periods. The age-specific PGS predicts an increase of 4 drinking days per year per PGS standard deviation when modeled separately from the common factor PGS in adulthood. The current work was underpowered at all steps of the analysis plan. Though small sample sizes and low statistical power limit the substantive conclusions that can be drawn regarding these research questions, this work provides a foundation for future genetic studies of developmental variability in the genetic underpinnings of alcohol use behaviors and genetically-informed, age-matched phenotype prediction.

Determining the stability of genome-wide factors in BMI between ages 40 to 69 years

Genome-wide association studies (GWAS) have successfully identified common variants associated with BMI. However, the stability of aggregate genetic variation influencing BMI from midlife and beyond is unknown. By analysing 165,717 men and 193,073 women from the UKBiobank, we performed BMI GWAS on six independent five-year age intervals between 40 and 72 years. We then applied genomic structural equation modeling to test competing hypotheses regarding the stability of genetic effects for BMI. LDSR genetic correlations between BMI assessed between ages 40 to 73 were all very high and ranged 0.89 to 1.00. Genomic structural equation modeling revealed that molecular genetic variance in BMI at each age interval could not be explained by the accumulation of any age-specific genetic influences or autoregressive processes. Instead, a common set of stable genetic influences appears to underpin genome-wide variation in BMI from middle to early old age in men and women alike.

The influence of chromosome 4 on high ethanol consumption and blood pressure

The Spontaneously Hypertensive Rats (SHR) strain was developed through selective breeding for high systolic blood pressure. In our laboratory, we established a congenic rat strain named SHR.Lewis-Anxrr16 (SLA16). The SLA16 rat strain is genetically identical to the SHR except for the inserted Anxrr16 region in chromosome 4. Our objective was to evaluate the influence of this genomic region on ethanol consumption and blood pressure. First, we exposed SHR and SLA16 male and female rats to ethanol consumption. Results showed that, regardless of strain, females consumed more ethanol than males during forced (10% v/v) and spontaneous ethanol consumption (SEC; 2.5-20% v/v). Then, females from both strains were used to evaluate sensitivity to ethanol. No strain differences in the loss of righting reflex were observed after ethanol treatment (3 g/kg, 20% w/v, intraperitoneal [i.p.]). But, in the triple test, female SHR rats presented lower sensitivity to the ethanol (1.2 g/kg, 14% w/v, i.p.). Surprisingly, female SHR rats also presented higher blood pressure after SEC (10% v/v). Finally, losartan treatment was effective in decreasing the blood pressure of female rats of both strains, but had specific effects on SHR ethanol consumption. Our data suggest that SLA16 female rats consume less ethanol (10%), are more sensitive to its effects, and present lower blood pressure than SHR female rats. We demonstrated that the Anxrr16 locus in chromosome 4 is a genetic candidate to explain high ethanol consumption and blood pressure, at least in females.

Reward Deficiency Syndrome (RDS): A Cytoarchitectural Common Neurobiological Trait of All Addictions

Alcohol and other substance use disorders share comorbidity with other RDS disorders, i.e., a reduction in dopamine signaling within the reward pathway. RDS is a term that connects addictive, obsessive, compulsive, and impulsive behavioral disorders. An estimated 2 million individuals in the United States have opioid use disorder related to prescription opioids. It is estimated that the overall cost of the illegal and legally prescribed opioid crisis exceeds one trillion dollars. Opioid Replacement Therapy is the most common treatment for addictions and other RDS disorders. Even after repeated relapses, patients are repeatedly prescribed the same opioid replacement treatments. A recent JAMA report indicates that non-opioid treatments fare better than chronic opioid treatments. Research demonstrates that over 50 percent of all suicides are related to alcohol or other drug use. In addition to effective fellowship programs and spirituality acceptance, nutrigenomic therapies (e.g., KB220Z) optimize gene expression, rebalance neurotransmitters, and restore neurotransmitter functional connectivity. KB220Z was shown to increase functional connectivity across specific brain regions involved in dopaminergic function. KB220/Z significantly reduces RDS behavioral disorders and relapse in human DUI offenders. Taking a Genetic Addiction Risk Severity (GARS) test combined with a the KB220Z semi-customized nutrigenomic supplement effectively restores dopamine homeostasis (WC 199).

Maternal Parenting Behaviors Amplify Environmental Influences on Developmental Trajectories of Alcohol Use During Adolescence

Compared to peer alcohol use, less is known on how parenting practices may modify genetic and environmental contributions to alcohol use longitudinally across adolescence. This study examined whether two maternal parenting behaviors, supervision and harsh parenting, may suppress or amplify genetic and environmental influences on three distinct developmental trajectories of adolescent alcohol use: normative increasing, early-onset, and low trajectories. Participants were drawn from a longitudinal study of a population-based twin sample (N = 842, 84% European descent, 52.7% female). Adolescents self-reported their past year alcohol use at ages 13, 14, 15, and 17 years, and their mothers reported their supervision and harsh parenting when twins were 13, 15, and 17 years old. Maternal supervision amplified non-shared environmental influence on the normative increasing and early-onset trajectories, whereas maternal harsh parenting amplified shared environmental influence on the early-onset trajectory and non-shared environmental influence on the low trajectory, respectively. The findings suggest maternal parenting practices as a potent developmental context that modulates the environmental influences of other proximal processes on adolescent alcohol use, and suggest that family-based parenting-focused intervention could be especially beneficial for adolescents following the early-onset trajectory.

Genetic and shared couple environmental contributions to smoking and alcohol use in the UK population

Alcohol use and smoking are leading causes of death and disability worldwide. Both genetic and environmental factors have been shown to influence individual differences in the use of these substances. In the present study we tested whether genetic factors, modelled alongside common family environment, explained phenotypic variance in alcohol use and smoking behaviour in the Generation Scotland (GS) family sample of up to 19,377 individuals. SNP and pedigree-associated effects combined explained between 18 and 41% of the variance in substance use. Shared couple effects explained a significant amount of variance across all substance use traits, particularly alcohol intake, for which 38% of the phenotypic variance was explained. We tested whether the within-couple substance use associations were due to assortative mating by testing the association between partner polygenic risk scores in 34,987 couple pairs from the UK Biobank (UKB). No significant association between partner polygenic risk scores were observed. Associations between an individual's alcohol PRS (b = 0.05, S.E. = 0.006, p < 2 × 10-16) and smoking status PRS (b = 0.05, S.E. = 0.005, p < 2 × 10-16) were found with their partner's phenotype. In support of this, G carriers of a functional ADH1B polymorphism (rs1229984), known to be associated with greater alcohol intake, were found to consume less alcohol if they had a partner who carried an A allele at this SNP. Together these results show that the shared couple environment contributes significantly to patterns of substance use. It is unclear whether this is due to shared environmental factors, assortative mating, or indirect genetic effects. Future studies would benefit from longitudinal data and larger sample sizes to assess this further.

The Associations of Polygenic Scores for Risky Behaviors and Parenting Behaviors with Adolescent Externalizing Problems

The current study focused on longitudinal effects of genetics and parental behaviors and their interplay on externalizing behaviors in a panel study following individuals from adolescence to young adulthood. The nationally representative sample of Add Health participants of European ancestry included N = 4142 individuals, measured on three occasions. Parenting was operationalized as experiences with child maltreatment and maternal closeness. Externalizing problems were operationalized as alcohol use, cannabis use, and antisocial behaviors. Genetic effects were operationalized as a polygenic score (PGS) of risky behaviors. The results showed significant effects for child maltreatment, maternal closeness, and PGS, above and beyond other factors and previous levels of externalizing behaviors. Furthermore, maternal closeness was found to negatively correlate with PGS. No significant interaction effects of parenting and PGS were found. The results underscore the joint independent effects of parenting and genetics on the change in externalizing behaviors from adolescence to young adulthood.

Peer Alcohol Use Differentially Amplifies Genetic and Environmental Effects on Different Developmental Trajectories of Adolescent Alcohol Use

PURPOSE

The purpose of the study was to investigate how peer alcohol use moderates genetic and environmental influences on three different developmental trajectories of alcohol use during adolescence: low (continuously low levels of use), early-onset fast-escalating (initiated use early, the level of use increased quickly), and normative increasing (started at a low level and increased steadily) using biometric modeling.

METHODS

Data were from a longitudinal study on a sample of population-based adolescent twins (N = 842, 52.7% female, 84% European Caucasian). Adolescents self-reported past-year alcohol use at age 13, 14, 15, and 17 years. Adolescents' nominated friends reported their own past-year alcohol use at age 13, 15, and 17 years.

RESULTS

Genetic and environmental influences on adolescents' alcohol use trajectories were differentially moderated by friends' alcohol use in different trajectories. Gene-environment interaction was implicated in the low and early-onset trajectories, such that genetic contributions were amplified when friends used more alcohol. Environment-environment interaction was involved in the normative increasing and early-onset trajectories, such that person-specific environmental contributions were amplified when friends' alcohol use increased.

CONCLUSIONS

Adolescent alcohol use remains a major public health issue, with peer alcohol use being a major risk factor. These findings suggest that close supervision to reduce deviant peer affiliation as well as preventions targeting peer group norms of alcohol use might be especially beneficial for adolescents following the normative increasing and early-onset trajectories.

Genetic and environmental influences on developmental trajectories of adolescent alcohol use

Adolescent alcohol use demonstrates distinct developmental trajectories with different times of onset, levels, and rates of growth. Twin research on adolescent alcohol use has shown that genetic influences are consistent with a gradual growth of risks, whereas non-shared environmental influences are more consistent with an accumulation of risks over time. The current study investigated the relative contributions of genetic and environmental influences on shaping different developmental trajectories of alcohol use through adolescence. Self-reported past year alcohol use was collected from 877 Canadian twins (47.1% males) at age 13, 14, 15, and 17 years. Growth mixture models were fit to examine different developmental trajectories of alcohol use, and biometric liability threshold models were fit to investigate genetic and environmental influences on the liability of belonging to identified trajectories. Three trajectories were identified: low (15.1%), early onset (8.2%), and normative increasing (76.7%). Memberships in the low and early-onset group were under genetic (27.6% and 34.7%), shared (42.4% and 21.5%), and non-shared environment influences (30.0% and 43.8%). Membership in the normative increasing group was under genetic (37.7%) and non-shared environment influences (62.3%). Non-shared environmental influences were significantly larger for the normative increasing trajectory than for the low trajectory. These findings provide a more refined picture of genetic and environmental influences in the development of alcohol use in subgroups of adolescents. Genetic and environmental influences both matter, but to different degrees in different trajectories. Future research should identify specific shared and non-shared environmental experiences that distinguish different trajectories.

The Genetics of Externalizing Problems

Externalizing problems generally refer to a constellation of behaviors and/or disorders characterized by impulsive action and behavioral disinhibition. Phenotypes on the externalizing spectrum include psychiatric disorders, nonclinical behaviors, and personality characteristics (e.g. alcohol use disorders, other illicit substance use, antisocial behaviors, risky sex, sensation seeking, among others). Research using genetic designs including latent designs from twin and family data and more recent designs using genome-wide data reveal that these behaviors and problems are genetically influenced and largely share a common genetic etiology. Large-scale gene-identification efforts have started to identify robust associations between genetic variants and these phenotypes. However, there is still considerable work to be done. This chapter provides an overview of the current state of research into the genetics of behaviors and disorders on the externalizing spectrum.

The gene-environmental architecture of the development of adolescent substance use

BACKGROUND

Using a longitudinal twin design and a latent growth curve/autoregressive approach, this study examined the genetic-environmental architecture of substance use across adolescence.

METHODS

Self-reports of substance use (i.e. alcohol, marijuana) were collected at ages 13, 14, 15, and 17 years from 476 twin pairs (475 boys, 477 girls) living in the Province of Quebec, Canada. Substance use increased linearly across the adolescent years.

RESULTS

ACE modeling revealed that genetic, as well as shared and non-shared environmental factors explained the overall level of substance use and that these same factors also partly accounted for growth in substance use from age 13 to 17. Additional genetic factors predicted the growth in substance use. Finally, autoregressive effects revealed age-specific non-shared environmental influences and, to a lesser degree, age-specific genetic influences, which together accounted for the stability of substance use across adolescence.

CONCLUSIONS

The results support and expand the notion that genetic and environmental influences on substance use during adolescence are both developmentally stable and developmentally dynamic.