Polymorphic variation in the dopamine D4 receptor predicts delay discounting as a function of childhood socioeconomic status: evidence for differential susceptibility

The impact of poverty and socioeconomic status on brain, behaviour, and development: a unified framework

In this article, we, for the first time, provide a comprehensive overview and unified framework of the impact of poverty and low socioeconomic status (SES) on the brain and behaviour. While there are many studies on the impact of low SES on the brain (including cortex, hippocampus, amygdala, and even neurotransmitters) and behaviours (including educational attainment, language development, development of psychopathological disorders), prior studies did not integrate behavioural, educational, and neural findings in one framework. Here, we argue that the impact of poverty and low SES on the brain and behaviour are interrelated. Specifically, based on prior studies, due to a lack of resources, poverty and low SES are associated with poor nutrition, high levels of stress in caregivers and their children, and exposure to socio-environmental hazards. These psychological and physical injuries impact the normal development of several brain areas and neurotransmitters. Impaired functioning of the amygdala can lead to the development of psychopathological disorders, while impaired hippocampus and cortex functions are associated with a delay in learning and language development as well as poor academic performance. This in turn perpetuates poverty in children, leading to a vicious cycle of poverty and psychological/physical impairments. In addition to providing economic aid to economically disadvantaged families, interventions should aim to tackle neural abnormalities caused by poverty and low SES in early childhood. Importantly, acknowledging brain abnormalities due to poverty in early childhood can help increase economic equity. In the current study, we provide a comprehensive list of future studies to help understand the impact of poverty on the brain.

Main Biological Models of Resilience

Objective

Resilience is a complex process of adaptation to new conditions that would permit a positive outcome after adversities, traumas or other sources of stress. However, despite the growing interest in this topic, there is no universally accepted definition and no comprehensive bio-behavioural model. This systematic review aims to provide an overview of the main biological models that have been theorized to date, with a focus on new alternative theories to improve our understanding of the mechanisms underlying the development and strengthening of resilience, with potential implications for the prevention of some psychopathological disorders.

Method

This review was conducted according to PRISMA guidelines and includes 185 studies published in English in PubMed and Embase up to December 2023.

Results

Most studies use the stress-related model, which conceptualizes resilience as the absence of symptoms after the stressful event and mainly deal with the differences between stress-prone and resilient phenotypes in animals exposed to stress. However, the results of this search seem to suggest that resilience might be an independent construct with biological bases rooted in the stress system and the social brain, and widely sculptured by individual and environmental factors, especially early life events and affiliation.

Conclusions

This work contributes to ongoing efforts to understand the intricate mechanisms of resilience, while highlighting the potential of improving social relationships since our birth to promote coping strategies towards stress and traumas, and even a peaceful world.

Individuals being high in their sensitivity to the environment: Are sensitive period changes in play?

All individuals on planet earth are sensitive to the environment, but some more than others. These individual differences in sensitivity to environments are seen across many animal species including humans, and can influence personalities as well as vulnerability and resilience to mental disorders. Yet, little is known about the underlying brain mechanisms. Key genes that contribute to individual differences in environmental sensitivity are the serotonin transporter, dopamine D4 receptor and brain-derived neurotrophic factor genes. By synthesizing neurodevelopmental findings of these genetic factors, and discussing them through the lens of mechanisms related to sensitive periods, which are phases of heightened neuronal plasticity during which a certain network is being finetuned by experiences, we propose that these genetic factors delay but extend postnatal sensitive periods. This may explain why sensitive individuals show behavioral features that are characteristic of a young brain state at the level of sensory information processing, such as reduced filtering or blockade of irrelevant information, resulting in a sensory processing system that 'keeps all options open'.

The Moderating Role of the DYX1C1 Gene in the Effect of Home Supervision on Chinese Children's Reading Achievements: Evidence from the Diathesis-Stress Model

The current study aimed to explore whether susceptible children (with differences in DYX1C1 (dyslexia susceptibility 1 candidate gene 1) gene) are more likely to be influenced by either supportive or adverse home supervision in their reading achievements. Home supervision, reading achievements, and genotype data were collected from a total of 745 fourth and fifth grade children and their parents in Chongqing, China. The results showed that there was a significant interaction between the rs11629841 polymorphism of the DYX1C1 gene and home supervision on children's reading achievements. A further analysis based on the re-parameterized regression model showed that the interaction best fit a weak diathesis-stress model, which indicated that the home supervision had a stronger predictive effect on children's reading achievements among children with the susceptible genotype than children with a non-susceptible genotype in a more adverse environment rather than in a supportive environment. These results suggested that children carrying different genotypes may need targeted interventions and that their parents should emphasize home supervision to develop their children's reading skills.

Early musical training benefits to non-musical cognitive ability associated with the Gestalt principles

Musical training has been evidenced to facilitate music perception, which refers to the consistencies, boundaries, and segmentations in pieces of music that are associated with the Gestalt principles. The current study aims to test whether musical training is beneficial to non-musical cognitive ability with Gestalt principles. Three groups of Chinese participants (with early, late, and no musical training) were compared in terms of their performances on the Motor-Free Visual Perception Test (MVPT). The results show that the participants with early musical training had significantly better performance in the Gestalt-like Visual Closure subtest than those with late and no musical training, but no significances in other Gestalt-unlike subtests was identified (Visual Memory, Visual Discrimination, Spatial Relationship, Figure Ground in MVPT). This study suggests the benefit of early musical training on non-musical cognitive ability with Gestalt principles.

Cumulative genetic score of KIAA0319 affects reading ability in Chinese children: moderation by parental education and mediation by rapid automatized naming

KIAA0319, a well-studied candidate gene, has been shown to be associated with reading ability and developmental dyslexia. In the present study, we investigated whether KIAA0319 affects reading ability by interacting with the parental education level and whether rapid automatized naming (RAN), phonological awareness and morphological awareness mediate the relationship between KIAA0319 and reading ability. A total of 2284 Chinese children from primary school grades 3 and 6 participated in this study. Chinese character reading accuracy and word reading fluency were used as measures of reading abilities. The cumulative genetic risk score (CGS) of 13 SNPs in KIAA0319 was calculated. Results revealed interaction effect between CGS of KIAA0319 and parental education level on reading fluency. The interaction effect suggested that individuals with a low CGS of KIAA0319 were better at reading fluency in a positive environment (higher parental educational level) than individuals with a high CGS. Moreover, the interaction effect coincided with the differential susceptibility model. The results of the multiple mediator model revealed that RAN mediates the impact of the genetic cumulative effect of KIAA0319 on reading abilities. These findings provide evidence that KIAA0319 is a risk vulnerability gene that interacts with environmental factor to impact reading abilities and demonstrate the reliability of RAN as an endophenotype between genes and reading associations.

Altered delay discounting in neurodegeneration: insight into the underlying mechanisms and perspectives for clinical applications

Steeper delay discounting (i.e., the extent to which future rewards are perceived as less valuable than immediate ones) has been proposed as a transdiagnostic process across different health conditions, in particular psychiatric disorders. Impulsive decision-making is a hallmark of different neurodegenerative conditions but little is known about delay discounting in the domain of neurodegenerative conditions. We reviewed studies on delay discounting in patients with Parkinson's disease (PD) and in patients with dementia (Alzheimer's disease / AD or frontotemporal dementia / FTD). We proposed that delay discounting could be an early marker of the neurodegenerative process. We developed the idea that altered delay discounting is associated with overlapping but distinct neurocognitive mechanisms across neurodegenerative diseases: dopaminergic-related disorders of reward processing in PD, memory/projection deficits due to medial temporal atrophy in AD, modified reward processing due to orbitofrontal atrophy in FTD. Neurodegeneration could provide a framework to decipher the neuropsychological mechanisms of value-based decision-making. Further, delay discounting could become a marker of interest in clinical practice, in particular for differential diagnosis.

Individual differences in decision-making: evidence for the scarcity hypothesis from the English Longitudinal Study of Ageing

We report the results of a pre-registered analysis of data from the English Longitudinal Study of Ageing that was designed to test the hypothesis that economic scarcity is associated with individual differences in decision-making. We tested this hypothesis by comparing time preferences for different socio-economic groups and in geographical areas ranging from the most deprived to the least deprived in England using the English indices of multiple deprivation. The data supported this hypothesis: people in the most deprived areas were more likely to prefer smaller-sooner rewards than people from the least deprived areas. Similarly, people in technical or routine occupations tended to prefer smaller-sooner rewards than people in professional or intermediate occupations. In addition, we found that gender, cognitive function and subjective social status also predicted time preferences. We discuss these results in the context of theoretical models of scarcity-based models of choice behaviour and decision-making.

Systemic Inflammation Contributes to the Association Between Childhood Socioeconomic Disadvantage and Midlife Cardiometabolic Risk

BACKGROUND

Childhood socioeconomic disadvantage is associated with increased risk for chronic inflammation and cardiometabolic disease at midlife.

PURPOSE

As it is presently unknown whether inflammation mediates the relationship between childhood socioeconomic status (SES) and adulthood cardiometabolic risk, we investigated associations between retrospectively reported childhood SES, circulating levels of inflammatory markers, and a latent construct of cardiometabolic risk in midlife adults.

METHODS

Participants were 1,359 healthy adults aged 30-54 (Adult Health and Behavior Iⅈ 52% women, 17% Black) who retrospectively reported childhood SES (parental education, occupational grade). Measures included plasma interleukin (IL)-6, C-reactive protein (CRP), and cardiometabolic risk factors. Structural equation modeling was conducted, with cardiometabolic risk modeled as a second-order latent variable with adiposity, blood lipids, glucose control, and blood pressure as first-order components.

RESULTS

Lower childhood SES was associated with greater risk for cardiometabolic disease at midlife (β = -0.08, CI[-0.04, -0.01], p = .01) in models adjusted for demographics, but this association was attenuated in models that adjusted for adulthood SES and health behaviors. In fully-adjusted models, the relationship between lower childhood SES and adult cardiometabolic risk was partially explained by higher circulating levels of CRP (β = -0.05, CI[-0.02, -0.01], p = .001), but not by IL-6. In an exploratory model, lower adulthood SES was also found to independently contribute to the association between childhood SES and adult cardiometabolic risk (β = -0.02, CI[-0.01, -0.001], p = .02).

CONCLUSIONS

The current study provides initial evidence that systemic inflammation may contribute to childhood socioeconomic disparities in cardiometabolic risk in midlife. Future work would benefit from prospective investigation of these relationships.

The role of primary school composition in affective decision-making: a prospective cohort study

PURPOSE

School-level characteristics are known to be associated with pupils' academic and cognitive ability but also their socioemotional development. This study examines, for the first time, whether primary school characteristics are associated with pupils' affective decision-making too.

METHODS

The sample included 3,141 children participating in the Millennium Cohort Study with available data on their school's characteristics, according to the National Pupil Database, at age 7 years. Decision-making was measured using the Cambridge Gambling Task at age 11 years. We modelled data using a series of sex-stratified linear regression analyses of decision-making (risk-taking, quality of decision-making, risk adjustment, deliberation time, and delay aversion) against four indicators of school composition (academic performance and proportions among pupils who are native speakers of English, are eligible for free school meals and have special educational needs).

RESULTS

After adjustment for individual and family-level confounding, schools with a higher average academic performance showed more delay aversion among males, and among females, higher deliberation time and lower risk-taking. Schools with proportionally more native English speakers had higher deliberation time among males. Schools with proportionally more pupils eligible for free school meals showed lower scores on quality of decision-making among males. Schools with proportionally more children with special educational needs showed better quality of decision-making among males and lower risk-taking among females.

CONCLUSION

The findings of this study can be used to target support for primary schools. Interventions aiming to support lower-achieving schools and those with less affluent intakes could help to improve boys' affective decision-making.

Heteromerization between α2A adrenoceptors and different polymorphic variants of the dopamine D4 receptor determines pharmacological and functional differences. Implications for impulsive-control disorders

Polymorphic alleles of the human dopamine D₄ receptor gene (DRD4) have been consistently associated with individual differences in personality traits and neuropsychiatric disorders, particularly between the gene encoding dopamine D_4.7 receptor variant and attention deficit hyperactivity disorder (ADHD). The α_2A adrenoceptor gene has also been associated with ADHD. In fact, drugs targeting the α_2A adrenoceptor (α_2AR), such as guanfacine, are commonly used in ADHD treatment. In view of the involvement of dopamine D₄ receptor (D₄R) and α_2AR in ADHD and impulsivity, their concurrent localization in cortical pyramidal neurons and the demonstrated ability of D₄R to form functional heteromers with other G protein-coupled receptors, in this study we evaluate whether the α_2AR forms functional heteromers with D₄R and weather these heteromers show different properties depending on the D₄R variant involved. Using cortical brain slices from hD_4.7R knock-in and wild-type mice, here, we demonstrate that α_2AR and D₄R heteromerize and constitute a significant functional population of cortical α_2AR and D₄R. Moreover, in cortical slices from wild-type mice and in cells transfected with α_2AR and D_4.4R, we detect a negative crosstalk within the heteromer. This negative crosstalk is lost in cortex from hD_4.7R knock-in mice and in cells expressing the D_4.7R polymorphic variant. We also show a lack of efficacy of D₄R ligands to promote G protein activation and signaling only within the α_2AR-D_4.7R heteromer. Taken together, our results suggest that α_2AR-D₄R heteromers play a pivotal role in catecholaminergic signaling in the brain cortex and are likely targets for ADHD pharmacotherapy.

Individual Differences in Intertemporal Choice

Intertemporal choice involves deciding between smaller, sooner and larger, later rewards. People tend to prefer smaller rewards that are available earlier to larger rewards available later, a phenomenon referred to as temporal or delay discounting. Despite its ubiquity in human and non-human animals, temporal discounting is subject to considerable individual differences. Here, we provide a critical narrative review of this literature and make suggestions for future work. We conclude that temporal discounting is associated with key socio-economic and health-related variables. Regarding personality, large-scale studies have found steeper temporal discounting to be associated with higher levels of self-reported impulsivity and extraversion; however, effect sizes are small. Temporal discounting correlates negatively with future-oriented cognitive styles and inhibitory control, again with small effect sizes. There are consistent associations between steeper temporal discounting and lower intelligence, with effect sizes exceeding those of personality or cognitive variables, although socio-demographic moderator variables may play a role. Neuroimaging evidence of brain structural and functional correlates is not yet consistent, neither with regard to areas nor directions of effects. Finally, following early candidate gene studies, recent Genome Wide Association Study (GWAS) approaches have revealed the molecular genetic architecture of temporal discounting to be more complex than initially thought. Overall, the study of individual differences in temporal discounting is a maturing field that has produced some replicable findings. Effect sizes are small-to-medium, necessitating future hypothesis-driven work that prioritizes large samples with adequate power calculations. More research is also needed regarding the neural origins of individual differences in temporal discounting as well as the mediating neural mechanisms of associations of temporal discounting with personality and cognitive variables.

Steep Discounting of Future Rewards as an Impulsivity Phenotype: A Concise Review

This chapter provides an overview over the behavioral economic index of impulsivity known as delay discounting. Specifically, delay discounting refers to an individual's preference for smaller immediate rewards over a larger delayed rewards. The more precipitously an individual discounts future rewards, the more impulsive they are considered to be. First, the chapter reviews the nature of delay discounting as a psychological process and juxtaposes it with nominally similar processes, including other facets of impulsivity. Second, the chapter reviews the links between delay discounting and numerous health behaviors, including addiction, attention deficit/hyperactivity disorder, and obesity. Third, the determinants of individual variation in delay discounting are discussed, including both genetic and environmental contributions. Finally, the chapter evaluates delay discounting as a potentially modifiable risk factor and the status of clinical interventions designed to reduce delay discounting to address deficits in self-control in a variety of maladaptive behaviors.

Elaborating on premature adolescent autonomy: Linking variation in daily family processes to developmental risk

This study revisits the premature autonomy model by examining parents' use of positive behavior support (PBS) practices on a daily timescale to better understand underlying processes in developmental changes in family disengagement and the implications for adolescent problem behavior and substance use. This study included 151 9th and 10th grade adolescents (61.5% female) and their caregivers, who participated in a baseline assessment, a 21-day daily diary burst, and a 1-year follow-up assessment. Four key findings emerged: (a) on days when parents used more PBS, adolescents felt more close and connected to their caregivers; (b) adolescents who exhibited a larger-magnitude of change in connectedness with caregivers in relation to variation in positive parenting (termed fragile connectedness) were at higher risk for antisocial behavior, deviant peer involvement, and substance use one year later; (c) individual differences in initial levels of antisocial behavior and effortful control accounted for between-person variation in fragile connectedness; and (d) day-level adolescent anger and parent-adolescent conflict predicted within-family variation in parents' use of PBS. Implications for the premature autonomy model and intervention science are discussed.

Circulating Interleukin-6 concentration covaries inversely with self-reported sleep duration as a function of polymorphic variation in the glucocorticoid receptor

Growing evidence links extremes of self-reported sleep duration with higher circulating markers of inflammatory disease risk, although not all findings are consistent. Extremes of sleep duration also associate with activation of the hypothalamic-pituitary-adrenocortical (HPA) system and the peripheral release of cortisol, a glucocorticoid (GC) important in downregulating transcription of pro-inflammatory molecules. Polymorphic variation in the gene encoding the GC receptor (GR; NR3C1) modulates cellular sensitivity to GC-mediated anti-inflammatory signaling, thereby affecting levels of pro-inflammatory molecules. Thus, we hypothesized that extremes of self-reported sleep duration may covary with circulating levels of inflammatory markers as a function of allelic variation in NR3C1. Specifically, we examine the possibility that a single nucleotide polymorphism of the GR gene-(rs6198), the minor (G) allele of which confers reduced GR sensitivity-moderates an association of sleep duration with interleukin (IL)-6 and C-reactive protein (CRP) among a large sample (IL-6: N = 857; CRP: N = 929) of midlife community volunteers of European ancestry. Findings showed that sleep duration varied inversely with IL-6 (β = -0.087, p = .012), and this association was stronger among individuals homozygous for the rs6198 G-allele compared to alternate genotypes (β = -0.071, p = .039). We also found that sleep duration showed a U-shaped association with CRP (polynomial term: β = 0.093, p = .006), which was not moderated by rs6198 genotype. In conclusion, we show that a common genetic variant in the GR moderates an inverse association of self-reported sleep duration with circulating IL-6, possibly contributing to the increased disease risk observed among some short sleepers.

The interplay of polygenic plasticity and adrenocortical activity as sources of variability in pathways among family adversity, youth emotional reactivity, and psychological problems

This study examined the interplay between a polygenic composite and cortisol activity as moderators of the mediational pathway among family adversity, youth negative emotional reactivity to family conflict, and their psychological problems. The longitudinal design contained three annual measurement occasions with 279 adolescents (Mean age = 13.0 years) and their parents. Latent difference score analyses indicated that observational ratings of adversity in interparental and parent-child interactions at Wave 1 predicted increases in a multimethod, multi-informant assessment of youth negative emotional reactivity to family conflict from Waves 1 to 2. Changes in youth negative emotional reactivity, in turn, predicted increases in a multi-informant (i.e., parents, adolescent, and teacher) assessment of psychological problems from Waves 1 to 3. Consistent with differential susceptibility theory, the association between family adversity and negative emotional reactivity was stronger for adolescents who carried more sensitivity alleles in a polygenic composite consisting of 5-HTTLPR, DRD4 VNTR, and BDNF polymorphisms. Analyses of adolescent cortisol in the period surrounding a family disagreement task at Wave 1 revealed that overall cortisol output, rather than cortisol reactivity, served as an endophenotype of the polygenic composite. Overall cortisol output was specifically associated with polygenic plasticity and moderated the association between family adversity and youth negative emotional reactivity in the same for better or for worse manner as the genetic composite. Finally, moderator-mediated-moderation analyses indicated that the moderating role of the polygenic plasticity composite was mediated by the moderating role of adolescent cortisol output in the association between family adversity and their emotional reactivity.

Catechol-O-Methyltransferase Genotypes and Parenting Influence on Long-Term Executive Functioning After Moderate to Severe Early Childhood Traumatic Brain Injury: An Exploratory Study

OBJECTIVES

To examine catechol-O-methyltransferase (COMT) rs4680 genotypes as moderators of the effects of parenting style on postinjury changes in parent behavior ratings of executive dysfunction following moderate to severe early childhood traumatic brain injury.

SETTING

Research was conducted in an outpatient setting.

PARTICIPANTS

Participants included children admitted to hospital with moderate to severe traumatic brain injury (n = 55) or orthopedic injuries (n = 70) between ages 3 and 7 years.

DESIGN

Prospective cohort followed over 7 years postinjury.

MAIN MEASURES

Parenting Practices Questionnaire and the Behavior Rating Inventory of Executive Functioning obtained at baseline, 6, 12, and 18 months, and 3.5 and 6.8 years postinjury. DNA was collected from saliva samples, purified using the Oragene (DNA Genotek, Ottawa, Ontario, Canada) OG-500 self-collection tubes, and analyzed using TaqMan (Applied Biosystems, Thermo Fisher Scientific, Waltham, Massachusetts) assay protocols to identify the COMT rs4680 polymorphism.

RESULTS

Linear mixed models revealed a significant genotype × parenting style × time interaction (F = 5.72, P = .02), which suggested that the adverse effects of authoritarian parenting on postinjury development of executive functioning were buffered by the presence of the COMT AA genotype (lower enzyme activity, higher dopamine levels). There were no significant associations of executive functioning with the interaction between genotype and authoritative or permissive parenting ratings.

CONCLUSION

The lower activity COMT rs4680 genotype may buffer the negative effect of authoritarian parenting on long-term executive functioning following injury in early childhood. The findings provide preliminary evidence for associations of parenting style with executive dysfunction in children and for a complex interplay of genetic and environmental factors as contributors to decreases in these problems after traumatic injuries in children. Further investigation is warranted to understand the interplay among genetic and environmental factors related to recovery after traumatic brain injury in children.

Effects of reward and punishment on learning from errors in smokers

BACKGROUND

Punishing errors facilitates adaptation in healthy individuals, while aberrant reward and punishment sensitivity in drug-dependent individuals may change this impact. Many societies have institutions that use the concept of punishing drug use behavior, making it important to understand how drug dependency mediates the effects of negative feedback for influencing adaptive behavior.

METHODS

Using an associative learning task, we investigated differences in error correction rates of dependent smokers, compared with controls. Two versions of the task were administered to different participant samples: One assessed the effect of varying monetary contingencies to task performance, the other, the presence of reward as compared to avoidance of punishment for correct performance.

RESULTS

While smokers recalled associations that were rewarded with a higher value 11% more often than lower rewarded locations, they did not correct higher punished locations more often. Controls exhibited the opposite pattern. The three-way interaction between magnitude, feedback type and group was significant, F(1,48) = 5.288, p =0.026, ɳ²p =0.099. Neither participant group corrected locations offering reward more often than those offering avoidances of punishment. The interaction between group and feedback condition was not significant, F(1,58) = 0.0, p =0.99, ɳ²p =0.001.

CONCLUSIONS

The present results suggest that smokers have poorer learning from errors when receiving negative feedback. Moreover, larger rewards reinforce smokers' behavior stronger than smaller rewards, whereas controls made no distinction. These findings support the hypothesis that dependent smokers may respond to positively framed and rewarded anti-smoking programs when compared to those relying on negative feedback or punishment.

Leveraging delay discounting for health: Can time delays influence food choice?

Delay discounting, the tendency to choose smaller immediate rewards over larger delayed rewards, is theorized to promote consumption of immediately rewarding but unhealthy foods at the expense of long-term weight maintenance and nutritional health. An untested implication of delay discounting models of decision-making is that selectively delaying access to less healthy foods may promote selection of healthier (immediately available) alternatives, even if they may be less desirable. The current study tested this hypothesis by measuring healthy versus regular vending machine snack purchasing before and during the implementation of a 25-s time delay on the delivery of regular snacks. Purchasing was also examined under a $0.25 discount on healthy snacks, a $0.25 tax on regular snacks, and the combination of both pricing interventions with the 25-s time delay. Across 32,019 vending sales from three separate vending locations, the 25-s time delay increased healthy snack purchasing from 40.1% to 42.5%, which was comparable to the impact of a $0.25 discount (43.0%). Combining the delay and the discount had a roughly additive effect (46.0%). However, the strongest effects were seen under the $0.25 tax on regular snacks (53.7%) and the combination of the delay and the tax (50.2%). Intervention effects varied substantially between vending locations. Importantly, time delays did not harm overall vending sales or revenue, which is relevant to the real-world feasibility of this intervention. More investigation is needed to better understand how the impact of time delays on food choice varies across populations, evaluate the effects of time delays on beverage vending choices, and extend this approach to food choices in contexts other than vending machines.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02359916.

Influence of Catechol-O-methyltransferase on Executive Functioning Longitudinally After Early Childhood Traumatic Brain Injury: Preliminary Findings

OBJECTIVE

To elucidate the association of a functional catechol-O-methyltransferase (COMT) genotype (rs4680) with recovery of executive functions up to 18 months after early childhood traumatic brain injury (TBI) compared with an orthopedic injury (OI) group.

SETTING

Outpatient.

PARTICIPANTS

A total of 134 children with a moderate to severe TBI (n = 63) or OI (n = 71) between the ages of 3 and 6 years who were followed 18 months postinjury.

DESIGN

Case-comparison, longitudinal cohort

MAIN MEASURES

: The Behavior Rating Inventory of Executive Function, developmental NEuroPSYchological Assessment (NEPSY) of Verbal Fluency, and a modified Stroop Test for young children (Shape School).

RESULTS

The low-activity COMT enzyme genotype (AA) was associated with better scores on the developmental NEPSY of Verbal Fluency (F = 3.80; P = .02) and the Shape School (F = 2.89; P = .06) in all participants when controlling for injury type (TBI vs OI) over the first 18 months after injury. Injury type (TBI vs OI) did not significantly moderate the effect of the COMT genotypes on executive function recovery.

CONCLUSION

This study provides preliminary evidence for a role of COMT genotypes in long-term recovery of executive function after pediatric TBI and OI. Larger studies are needed to determine the exact link between genetic variation in the COMT gene and TBI recovery in children.

The link between deprivation and its behavioural constellation is confounded by genetic factors

Most research cited throughout Pepper & Nettle's (P&N's) target article is correlational and suffers from a serious genetic confound that renders it of little evidentiary value. Of correlational findings that are not confounded, P&N ignore examples that contradict their model. Further, P&N's claim that evolutionary models explaining between-species differences in behaviour can be used to understand that corresponding individual differences lack any evidence.

Neural dysfunction during temporal discounting in paediatric Attention-Deficit/Hyperactivity Disorder and Obsessive-Compulsive Disorder

Both Attention-Deficit/Hyperactivity Disorder (ADHD) and Obsessive-Compulsive Disorder (OCD) are associated with choice impulsivity, i.e. the tendency to prefer smaller immediate rewards over larger delayed rewards. However, the extent to which this impulsivity is mediated by shared or distinct underlying neural mechanisms is unclear. Twenty-six boys with ADHD, 20 boys with OCD and 20 matched controls (aged 12-18) completed an fMRI version of an individually adjusted temporal discounting (TD) task which requires choosing between a variable amount of money now or £100 in one week, one month or one year. Activations to immediate and delayed reward choices were compared between groups using a three-way ANCOVA. ADHD patients had steeper discounting rates on the task relative to controls. OCD patients did not differ from controls or patients with ADHD. Patients with ADHD and OCD showed predominantly shared activation deficits during TD in fronto-striato-insular-cerebellar regions responsible for self-control and temporal foresight, suggesting that choice impulsivity is mediated by overlapping neural dysfunctions in both disorders. OCD patients alone showed dysfunction relative to controls in right orbitofrontal and rostrolateral prefrontal cortex, extending previous findings of abnormalities in these regions in OCD to the domain of choice impulsiveness.

Developmental Patterns of Child Emotion Dysregulation as Predicted by Serotonin Transporter Genotype and Parenting

Individual differences in emotion regulation are central to social, academic, occupational, and psychological development, and emotion dysregulation (ED) in childhood is a risk factor for numerous developmental outcomes. The present study aimed to (a) describe the developmental trajectory of ED across early childhood (3-6 years) and (b) examine its sensitivity to youth serotonin transporter genotype, positive and negative parenting behaviors, and their interaction. Participants were 99 families in the Collaborative Family Study, a longitudinal study of children with or without developmental delays. Child ED and early parenting were coded from parent-child interactions. To examine serotonin transporter genotype as a moderator between parenting and child emotion dysregulation (ED), children with the homozygous short (SS) genotype were compared to children with the homozygous long (LL) or heterozygous (SL) genotype. We used latent growth curve modeling (LGCM) to model yearly change in ED from child age 3 to 6 years. LGCM revealed that ED decreased overall across early childhood. In addition, we observed separate Genotype × Positive and Genotype × Negative parenting behavior interactions in predictions of ED growth curves. Children with the SL/LL genotype had ED trajectories that were minimally related to positive and negative parenting behavior, whereas ED decreased more precipitously among children with the SS genotype when exposed to low negative parenting or high positive parenting. These findings provide evidence for Gene × Environment interactions (G×Es) in the development of ED in a manner that is conceptually consistent with vantage sensitivity, and they improve inferences afforded by prospective designs.

Epigenetic and Neural Circuitry Landscape of Psychotherapeutic Interventions

The science behind psychotherapy has garnered considerable interest, as objective measures are being developed to map the patient's subjective change over the course of treatment. Prenatal and early life influences have a lasting impact on how genes are expressed and the manner in which neural circuits are consolidated. Transgenerationally transmitted epigenetic markers as well as templates of enhanced thought flexibility versus evasion can be passed down from parent to child. This influences gene expression/repression (impacting neuroplasticity) and kindling of neurocircuitry which can perpetuate maladaptive cognitive processing seen in a number of psychiatric conditions. Importantly, genetic factors and the compounding effects of early life adversity do not inexorably lead to certain fated outcomes. The concepts of vulnerability and resilience are becoming more integrated into the framework of "differential susceptibility," speaking to how corrective environmental factors may promote epigenetic change and reconfigure neural templates, allowing for symptomatic improvement. Psychotherapy is one such factor, and this review will focus on our current knowledge of its epigenetic and neurocircuitry impact.

Effects of bonding with parents and home culture on intercultural adaptations and the moderating role of genes

In the current age of globalization, living abroad is becoming an increasingly common and highly sought after experience. Sojourners' ability to adjust to a new culture can be affected by their existing attachments, internalized as intrapsychic environment, as well as their biological sensitivity to environment. This sensitivity can be partly attributed to one's genomic endowments. As such, this prospective study sought to examine the differential effects of early experiences with parents and affection for home culture on young adults' ability to adapt to a foreign culture (n=305, students who studied overseas for a semester) - specifically, the difficulties they experience - moderated by genetic susceptibility. An additional 258 students who did not travel overseas were included as a comparison group to demonstrate the uniqueness of intercultural adaptation. Current findings suggest that the maternal, paternal and cultural bondings or affections affect different aspects of intercultural adjustment. Maternal bonding affected sojourners' relationships with host nationals, while paternal bonding affected sojourners' adjustment to a new physical environment. Moreover, individuals' genetic predispositions significantly moderate these main effects regarding how much difficulty the sojourners experienced overseas.

Applying Systems Biology Methodology To Identify Genetic Factors Possibly Associated with Recovery after Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide. It is linked with a number of medical, neurological, cognitive, and behavioral sequelae. The influence of genetic factors on the biology and related recovery after TBI is poorly understood. Studies that seek to elucidate the impact of genetic influences on neurorecovery after TBI will lead to better individualization of prognosis and inform development of novel treatments, which are considerably lacking. Current genetic studies related to TBI have focused on specific candidate genes. The objectives of this study were to use a system biology-based approach to identify biologic processes over-represented with genetic variants previously implicated in clinical outcomes after TBI and identify unique genes potentially related to recovery after TBI. After performing a systematic review to identify genes in the literature associated with clinical outcomes, we used the genes identified to perform a systems biology-based integrative computational analysis to ascertain the interactions between molecular components and to develop models for regulation and function of genes involved in TBI recovery. The analysis identified over-representation of genetic variants primarily in two biologic processes: response to injury (cell proliferation, cell death, inflammatory response, and cellular metabolism) and neurocognitive and behavioral reserve (brain development, cognition, and behavior). Overall, this study demonstrates the use of a systems biology-based approach to identify unique/novel genes or sets of genes important to the recovery process. Findings from this systems biology-based approach provide additional insight into the potential impact of genetic variants on the underlying complex biological processes important to TBI recovery and may inform the development of empirical genetic-related studies for TBI. Future studies that combine systems biology methodology and genomic, proteomic, and epigenetic approaches are needed in TBI.

The behavioural constellation of deprivation: Causes and consequences

Socioeconomic differences in behaviour are pervasive and well documented, but their causes are not yet well understood. Here, we make the case that a cluster of behaviours is associated with lower socioeconomic status (SES), which we call “the behavioural constellation of deprivation.” We propose that the relatively limited control associated with lower SES curtails the extent to which people can expect to realise deferred rewards, leading to more present-oriented behaviour in a range of domains. We illustrate this idea using the specific factor of extrinsic mortality risk, an important factor in evolutionary theoretical models. We emphasise the idea that the present-oriented behaviours of the constellation are a contextually appropriate response to structural and ecological factors rather than a pathology or a failure of willpower. We highlight some principles from evolutionary theoretical models that can deepen our understanding of how socioeconomic inequalities can become amplified and embedded. These principles are that (1) small initial disparities can lead to larger eventual inequalities, (2) feedback loops can embed early-life circumstances, (3) constraints can breed further constraints, and (4) feedback loops can operate over generations. We discuss some of the mechanisms by which SES may influence behaviour. We then review how the contextually appropriate response perspective that we have outlined fits with other findings about control and temporal discounting. Finally, we discuss the implications of this interpretation for research and policy.

Key role of the dopamine D4 receptor in the modulation of corticostriatal glutamatergic neurotransmission

Polymorphic variants of the dopamine D₄ receptor gene (DRD4) have been repeatedly associated with numerous neuropsychiatric disorders. Yet, the functional role of the D₄ receptor and the functional differences of the products of DRD4 polymorphic variants remained enigmatic. Immunohistochemical and optogenetic-microdialysis experiments were performed in knock-in mice expressing a D₄ receptor with the long intracellular domain of a human DRD4 polymorphic variant associated with attention deficit hyperactivity disorder (ADHD). When compared with the wild-type mouse D₄ receptor, the expanded intracellular domain of the humanized D₄ receptor conferred a gain of function, blunting methamphetamine-induced cortical activation and optogenetic and methamphetamine-induced corticostriatal glutamate release. The results demonstrate a key role of the D₄ receptor in the modulation of corticostriatal glutamatergic neurotransmission. Furthermore, these data imply that enhanced D₄ receptor-mediated dopaminergic control of corticostriatal transmission constitutes a vulnerability factor of ADHD and other neuropsychiatric disorders.

Gene and environment interaction: Is the differential susceptibility hypothesis relevant for obesity?

The differential susceptibility model states that a given genetic variant is associated with an increased risk of pathology in negative environments but greater than average resilience in enriched ones. While this theory was first implemented in psychiatric-genetic research, it may also help us to unravel the complex ways that genes and environments interact to influence feeding behavior and obesity. We reviewed evidence on gene vs. environment interactions that influence obesity development, aiming to support the applicability of the differential susceptibility model for this condition, and propose that various environmental "layers" relevant for human development should be considered when bearing the differential susceptibility model in mind. Mother-child relationship, socioeconomic status and individual's response are important modifiers of BMI and food intake when interacting with gene variants, "for better and for worse". While only a few studies to date have investigated obesity outcomes using this approach, we propose that the differential susceptibility hypothesis is in fact highly applicable to the study of genetic and environmental influences on feeding behavior and obesity risk.

Initial examination of priming tasks to decrease delay discounting

Steep discounting of delayed rewards is linked with a variety of unhealthy behaviors that contribute to the major causes of preventable death and disease. Growing evidence suggests that decreases in delay discounting contribute to healthier preferences. This study sought to provide preliminary evidence for the viability of developing a brief priming task to reduce delay discounting in a large, diverse group of individuals. Participants (n=1,122) were randomized to one of three conditions: Future Focus (FF), Present Focus (PF), and Non-Temporal Focus (NTF) intended respectively to decrease, increase, or have no effect on delay discounting. Participants then completed the Monetary Choice Questionnaire, a brief assessment of delay discounting rate. Participants randomized to FF exhibited significantly lower discounting rates than those randomized to PF or NTF conditions. Race, Hispanic background, social self-monitoring, education, and cigarette smoking also accounted for a significant amount of variance in the discounting model. These findings provide support for the development of a brief priming intervention that might be examined in clinical or public health contexts to decrease discounting and support healthy choices.

Genetic differential susceptibility on trial: meta-analytic support from randomized controlled experiments

The most stringent test of differential susceptibility theory is provided by randomized control trials examining the moderating role of genetic markers of differential susceptibility in experimental manipulations of the environment (Gene × Experimental Environment interactions), being at least 10 times more powerful than correlational Gene × Environment interaction studies. We identified 22 experiments involving 3,257 participants with various developmental outcomes (e.g., externalizing problems, internalizing behaviors, and cognitive development). Effect sizes contrasting experimental versus control group were computed both for subjects with the polymorphism considered indicative of heightened susceptibility (e.g., the dopamine receptor D4 gene seven-repeat allele and the serotonin transporter polymorphic region short allele) and others expected to be low in susceptibility (e.g., the dopamine receptor D4 gene four-repeat allele and the serotonin transporter polymorphic region short allele). Clear-cut experimental support for genetic differential susceptibility emerged: the combined effect size of the interventions for the susceptible genotypes amounted to r = .33 (95% confidence interval = 0.23, 0.42; p < .01) versus a nonsignificant r = .08 (95% confidence interval = -0.02, 0.17; p = .12) for the hypothesized nonsusceptible genotypes. Macrotrials showed more evidence of genetic differential susceptibility than microtrials, and differential susceptibility was more clearly observed in trials with externalizing and cognitive outcomes than with internalizing problems. This meta-analysis shows proof of principle for genetic differential susceptibility and indicates that it is time to explore its mechanisms and limits. The concept of differential susceptibility alters the idea of constitutional "risk" factors (reactive temperament and risk genotypes), and points to intervention efficacy hidden in Gene × Environment interactions.

Genetic and Neuroimaging Features of Personality Disorders: State of the Art

Personality disorders often act as a common denominator for many psychiatric problems, and studies on personality disorders contribute to the etiopathology, diagnosis, and treatment of many mental disorders. In recent years, increasing evidence from various studies has shown distinctive features of personality disorders, and that from genetic and neuroimaging studies has been especially valuable. Genetic studies primarily target the genes encoding neurotransmitters and enzymes in the serotoninergic and dopaminergic systems, and neuroimaging studies mainly focus on the frontal and temporal lobes as well as the limbic-paralimbic system in patients with personality disorders. Although some studies have suffered due to unclear diagnoses of personality disorders and some have included few patients for a given personality disorder, great opportunities remain for investigators to launch new ideas and technologies in the field.

Adolescent behavioral and neural reward sensitivity: a test of the differential susceptibility theory

Little is known about the causes of individual differences in reward sensitivity. We investigated gene-environment interactions (GxE) on behavioral and neural measures of reward sensitivity, in light of the differential susceptibility theory. This theory states that individuals carrying plasticity gene variants will be more disadvantaged in negative, but more advantaged in positive environments. Reward responses were assessed during a monetary incentive delay task in 178 participants with and 265 without attention-deficit/hyperactivity disorder (ADHD), from N=261 families. We examined interactions between variants in candidate plasticity genes (DAT1, 5-HTT and DRD4) and social environments (maternal expressed emotion and peer affiliation). HTTLPR short allele carriers showed the least reward speeding when exposed to high positive peer affiliation, but the most when faced with low positive peer affiliation or low maternal warmth. DAT1 10-repeat homozygotes displayed similar GxE patterns toward maternal warmth on general task performance. At the neural level, DRD4 7-repeat carriers showed the least striatal activation during reward anticipation when exposed to high maternal warmth, but the most when exposed to low warmth. Findings were independent of ADHD severity. Our results partially confirm the differential susceptibility theory and indicate the importance of positive social environments in reward sensitivity and general task performance for persons with specific genotypes.

Testing the Relations Among Family Disorganization, Delay Discounting, and Adolescent Alcohol Use: A Genetically Informed Study

BACKGROUND

Delay discounting is a potential etiological factor in adolescents' alcohol use, making it important to understand its antecedents. Family disorganization might contribute to delay discounting, but few studies have tested this relation. Moreover, because delay discounting is heritable, the effects of family disorganization on delay discounting might be moderated by adolescents' genetic risk for delay discounting. Thus, the current study examined the role of family disorganization, in interaction with genetic risk, in predicting adolescents' delay discounting and subsequent alcohol use.

METHODS

Adolescents participated in 4 waves of data collection. Adolescents self-reported their family disorganization at T1, completed a delay discounting questionnaire at T3, and self-reported their alcohol use both at T2 (covariate) and T4 (outcome). Using results from an independent sample, we created a polygenic risk score consisting of dopaminergic genes to index genetic risk for delay discounting.

RESULTS

Greater family disorganization predicted adolescents' greater delay discounting, but only for adolescents with low levels of genetic risk for delay discounting. Adolescents with high and mean levels of genetic risk for delay discounting showed elevated delay discounting regardless of their family's disorganization. Greater delay discounting prospectively predicted adolescents' greater alcohol use. Finally, the effects of family disorganization on adolescents' alcohol use were mediated through delay discounting, but only for adolescents with low levels of genetic risk.

CONCLUSIONS

Results suggest multiple pathways to delay discounting. Although there are genetically influenced pathways to delay discounting, family disorganization might represent an environmental pathway to delay discounting (and subsequent alcohol use) for a subset of adolescents at low genetic risk. These findings reinforce the utility of family interventions for reducing adolescents' delay discounting and alcohol use, at least for a subgroup of adolescents. Because higher family organization did not buffer against delay discounting among adolescents with high genetic risk, future research should explore other early environmental influences that could protect these high-risk adolescents from developing these risky behaviors.

Early life stress produces compulsive-like, but not impulsive, behavior in females

Adverse experiences during childhood are associated with the development of psychiatric disorders later in life. In particular, childhood abuse and neglect are risk factors for addictive disorders, such as substance misuse and pathological gambling. Impulsivity and compulsivity are key features of these disorders. Therefore, we investigated whether childhood adversity might increase vulnerability for addictive disorders through promotion of compulsive and impulsive behaviors. Rats were exposed to a brief, variable childhood or prepubertal stress protocol (Postnatal Days 25-27), and their behavior in a delay discounting task was compared with that of control animals in adulthood. Prepubertal stress produced compulsive-type behavior in females. Specifically, stressed females displayed inappropriate responses during a choice phase of the task, perseverating with nosepoke responding instead of choosing between 2 levers. Stressed females also showed learning impairments during task training. However, prepubertal stress was not associated with the development of impulsive behavior, as rates of delay discounting were not affected in either sex. Childhood adversity may contribute to the establishment and maintenance of addictive disorders by increasing perseveration in females. Perseverative behavior may therefore provide a viable therapeutic target for preventing the development of addictive disorders in individuals exposed to childhood adversity. These effects were not seen in males, highlighting sex differences in response to early life stress.

Delay discounting: Pigeon, rat, human--does it matter?

Delay discounting refers to the decrease in subjective value of an outcome as the time to its receipt increases. Across species and situations, animals discount delayed rewards, and their discounting is well-described by a hyperboloid function. The current review begins with a comparison of discounting models and the procedures used to assess delay discounting in nonhuman animals. We next discuss the generality of discounting, reviewing the effects of different variables on the degree of discounting delayed reinforcers by nonhuman animals. Despite the many similarities in discounting observed between human and nonhuman animals, several differences have been proposed (e.g., the magnitude effect; nonhuman animals discount over a matter of seconds whereas humans report willing to wait months, if not years before receiving a reward), raising the possibility of fundamental species differences in intertemporal choice. After evaluating these differences, we discuss delay discounting from an adaptationist perspective. The pervasiveness of discounting across species and situations suggests it is a fundamental process underlying decision making.

Reward devaluation: Dot-probe meta-analytic evidence of avoidance of positive information in depressed persons

Cognitive theories of depression and anxiety have traditionally emphasized the role of attentional biases in the processing of negative information. The dot-probe task has been widely used to study this phenomenon. Recent findings suggest that biased processing of positive information might also be an important aspect of developing psychopathological symptoms. However, despite some evidence suggesting persons with symptoms of depression and anxiety may avoid positive information, many dot-probe studies have produced null findings. The present review used conventional and novel meta-analytic methods to evaluate dot-probe attentional biases away from positive information and, for comparison, toward negative information, in depressed and anxious individuals. Results indicated that avoidance of positive information is a real effect exhibiting substantial evidential value among persons experiencing psychopathology, with individuals evidencing primary symptoms of depression clearly demonstrating this effect. Different theoretical explanations for these findings are evaluated, including those positing threat-processing structures, even-handedness, self-regulation, and reward devaluation, with the novel theory of reward devaluation emphasized and expanded. These novel findings and theory suggest that avoidance of prospective reward helps to explain the cause and sustainability of depressed states. Suggestions for future research and methodological advances are discussed.

Differential Susceptibility of the Developing Brain to Contextual Adversity and Stress

A swiftly growing volume of literature, comprising both human and animal studies and employing both observational and experimental designs, has documented striking individual differences in neurobiological sensitivities to environmental circumstances within subgroups of study samples. This differential susceptibility to social and physical environments operates bidirectionally, in both adverse and beneficial contexts, and results in a minority subpopulation with remarkably poor or unusually positive trajectories of health and development, contingent upon the character of environmental conditions. Differences in contextual susceptibility appear to emerge in early development, as the interactive and adaptive product of genetic and environmental attributes. This paper surveys what is currently known of the mechanisms or mediators of differential susceptibility, at the levels of temperament and behavior, physiological systems, brain circuitry and neuronal function, and genetic and epigenetic variation. It concludes with the assertion that differential susceptibility is inherently grounded within processes of biological moderation, the complexities of which are at present only partially understood.

Dopamine D4 receptor gene and religious affiliation correlate with dictator game altruism in males and not females: evidence for gender-sensitive gene × culture interaction

On a large sample of 2288 Han Chinese undergraduates, we investigated how religion and DRD4 are related to human altruistic giving behavior as measured with the Andreoni-Miller Dictator Game. This game enables us to clearly specify (non-)selfishness, efficiency, and fairness motives for sharing. Participants were further classified into religious categories (Christian, Buddhist-Tao, and No Religion) based on self-reports, and genotyped for the dopamine D4 receptor (DRD4) gene exon III VNTR. Our analysis revealed a significant interaction between religion and DRD4 correlated with giving behavior solely among males: Whereas no significant association between religion and sharing decisions was observed in the majority 4R/4R genotype group, a significant difference in giving behavior between Christian and non-Christian males was seen in the non-4R/4R group, with Christian men being overall more altruistic (less selfish and fairer) than non-Christian men. These results support the vantage sensitivity hypothesis regarding DRD4 that the non-4R/4R “susceptibility” genotype is more responsive to a positive environment provided by some religions.

Vantage Sensitivity: Environmental Sensitivity to Positive Experiences as a Function of Genetic Differences

A large number of gene-environment interaction studies provide evidence that some people are more likely to be negatively affected by adverse experiences as a function of specific genetic variants. However, such "risk" variants are surprisingly frequent in the population. Evolutionary analysis suggests that genetic variants associated with increased risk for maladaptive development under adverse environmental conditions are maintained in the population because they are also associated with advantages in response to different contextual conditions. These advantages may include (a) coexisting genetic resilience pertaining to other adverse influences, (b) a general genetic susceptibility to both low and high environmental quality, and (c) a coexisting propensity to benefit disproportionately from positive and supportive exposures, as reflected in the recent framework of vantage sensitivity. After introducing the basic properties of vantage sensitivity and highlighting conceptual similarities and differences with diathesis-stress and differential susceptibility patterns of gene-environment interaction, selected and recent empirical evidence for the notion of vantage sensitivity as a function of genetic differences is reviewed. The unique contribution that the new perspective of vantage sensitivity may make to our understanding of social inequality will be discussed after suggesting neurocognitive and molecular mechanisms hypothesized to underlie the propensity to benefit disproportionately from benevolent experiences.

Impulsive delayed reward discounting as a genetically-influenced target for drug abuse prevention: a critical evaluation

This review evaluates the viability of delayed reward discounting (DRD), an index of how much an individual devalues a future reward based on its delay in time, for genetically-informed drug abuse prevention. A review of the literature suggests that impulsive DRD is robustly associated with drug addiction and meets most of the criteria for being an endophenotype, albeit with mixed findings for specific molecular genetic influences. Several modes of experimental manipulation have been demonstrated to reduce DRD acutely. These include behavioral strategies, such as mindfulness, reward bundling, and episodic future thinking; pharmacological interventions, including noradrenergic agonists, adrenergic agonists, and multiple monoamine agonists; and neuromodulatory interventions, such as transcranial magnetic stimulation and transcranial direct current stimulation. However, the generalization of these interventions to positive clinical outcomes remains unclear and no studies to date have examined interventions on DRD in the context of prevention. Collectively, these findings suggest it would be premature to target DRD for genetically-informed prevention. Indeed, given the evidence of environmental contributions to impulsive DRD, whether genetically-informed secondary prevention would ever be warranted is debatable. Progress in identifying polymorphisms associated with DRD profiles could further clarify the underlying biological systems for pharmacological and neuromodulatory interventions, and, as a qualitatively different risk factor from existing prevention programs, impulsive DRD is worthy of investigation at a more general level as a novel and promising drug abuse prevention target.

Associations Between a Dopamine D4 Receptor Gene, Alcohol Use, and Sexual Behaviors among Female Adolescent African Americans

Adolescent African-American females are disproportionately impacted by HIV, thus there is a clear need to understand factors associated with increased HIV-risk behaviors among this vulnerable population. We sought to explore the association between a dopamine D4 receptor gene (DRD4), a genetic marker associated with natural variations in rewarding behaviors, and self-reported alcohol-use and sexual risk-behaviors, while controlling for other known correlates of risk-taking such as impulsivity, sensation seeking, and peer norms among a group of high-risk African American female adolescents to evaluate whether this biological factor enhances our understanding of patterns of risk in this vulnerable group.

The hidden efficacy of interventions: gene×environment experiments from a differential susceptibility perspective

The efficacy of interventions might be underestimated or even go undetected as a main effect when it is hidden in gene-by-environment (G×E) interactions. This review moves beyond the problems thwarting correlational G×E research to propose genetic differential susceptibility experiments. G×E experiments can test the bright side as well as the dark side of the moderating role of genotypes traditionally considered to represent vulnerability to negative conditions. The differential susceptibility model predicts that carriers of these risk genotypes profit most from interventions changing the environment for the better. The evolutionary background of G×E and differential susceptibility is discussed, and statistical methods for the analysis of differential susceptibility (versus diathesis stress) are reviewed. Then, based on results from 22 randomized G×E experiments, meta-analytic evidence for the differential susceptibility model is presented. Intervention effects are much stronger in the susceptible genotypes than in the nonsusceptible genotypes. The final sections suggest possibilities to broaden the G component in the G×E equation by including genetic pathways, and to broaden the E component by including methylation level and gene expression as promising ways to probe the concept of the environment more deeply and address the perennial issue of what works for whom.