Gene-Environment Interplay and Child Psychopathology Notes

Twin and Adoption Studies

• Behavior genetics uses twin and adoption studies to quantify genetic and non-genetic effects on traits, behaviors, and abilities.

• These studies offer insights into the interplay between genes and environment, recognizing that phenotypes are shaped by both genetic predispositions and environmental factors.

• The approach examines the similarity of relatives with differing genetic relatedness to estimate the relative contributions of genes and environment to observed traits.

• Greater phenotypic similarity among closer relatives suggests a stronger genetic influence, while differences among them point to environmental contributions.

Rationale of Behavior Genetics

• Genetically related individuals should exhibit phenotypic similarity in proportion to the degree of gene influence on behavior.

• Different familial relationships provide varying estimates of similarity:

  • Full siblings share approximately 50% of their genes and are generally more alike than cousins, who share less genetic material.

  • Identical (monozygotic or MZ) twins share 100% of their genes and are more alike than non-identical (dizygotic or DZ) twins and full siblings, who share about 50%.

  • Adopted children tend to resemble their biological parents more than their adoptive parents for genetically influenced traits, as they share genes but not the rearing environment.

Methods in Behavior Genetics

• Family Studies:

  • Examine the prevalence of a trait or disorder within families to identify patterns of inheritance.

  • Compare the frequency of a trait or disorder in relatives of affected individuals versus relatives of unaffected individuals to determine if there is a familial aggregation.

  • While family studies are consistent with genetic explanations, they cannot disentangle genetic and environmental factors, as families share both genes and environment.

  • Twin or adoption studies are needed to separate these factors and estimate their unique contributions.

• Twin Studies:

  • Monozygotic (MZ) twins share 100% of their genes, making them ideal for studying genetic influence.

  • Dizygotic (DZ) twins share approximately 50% of their genes, similar to full siblings, and provide a comparison group for MZ twins.

• Adoption Studies:

  • Adoptive parents provide the environment but share no genes with the child, allowing researchers to isolate environmental effects.

  • Biological parents share genes with the child but do not raise them, enabling the study of genetic influences separate from environmental factors.

Twin Study Methodology

• Compare the similarity between identical (MZ) and non-identical (DZ) twins on a particular trait or behavior.

• Analyze correlation coefficients to separate genetic and environmental influences on the trait.

• Formulas:

  • $rMZ = genes + shared\ environment$

  • $rDZ = \frac{1}{2} genes + shared\ environment$

Contributions of Early Behavior Genetic Studies

• Estimate the relative contribution of genetic and environmental influences on trait variation, providing insights into the nature-nurture debate.

• Evidence suggests genetic influence on nearly all psychological traits, including attitudes, cognitive ability, personality, and psychopathology.

• The magnitude of genetic influence varies by trait and age, with some traits being more heritable than others and heritability changing over the lifespan.

• Enable examination of the interrelationships between genetic and non-genetic factors, recognizing that genes and environment do not operate in isolation but interact in complex ways.

Interface of Genetic and Non-Genetic Influences

• Both genes and environment are essential for development; neither can operate without the other.

• Scarr & Weinberg (1980): "Everyone must have both a viable gene complement and an environment in which the genes can be expressed over development. No genes, no organism; no environment, no organism.” This highlights that genes provide the blueprint for development, but the environment is necessary for that blueprint to be realized.

• Genetic endowment may predispose individuals to environmental influences, leading to gene-environment interaction (GxE), where the effect of a gene depends on the environment, or vice versa.

• Genetics may drive selection or construction of compatible environments, resulting in gene-environment correlation (rGE), where individuals with certain genetic predispositions seek out or create environments that are correlated with those predispositions.

Gene-Environment Correlation (rGE)

• Genetic endowment may lead individuals to select or construct environments compatible with their genes, creating a correlation between genes and environment.

• Example: A child genetically predisposed to be good at sports is more likely to be in an environment that supports athletic performance (coaching, practice).

Three Types of rGE

• Passive:

  • Parents provide both genes and environment to their children.

  • Genes and environment are correlated because the child receives both from their parents.

• Evocative:

  • An individual elicits reactions from others based on their genotype.

  • Example: Smiley babies receive more attention, reinforcing social interaction.

  • Antisocial boys evoke hostile reactions from others, leading to a cycle of negative interactions.

• Active:

  • Individuals seek environments related to their genotype (niche-picking).

  • Occurs when there are many environmental opportunities and children make their own choices, particularly during adolescence.

Gene-Environment Correlation as a Reciprocal Process

• rGE leads to a magnification of behavior over time.

• Example: Aptitude in rugby leads to enjoyment and practice, resulting in improvement, team selection, coaching, and further improvement.

• Matt Ridley calls this "aptitude and appetite”, suggesting that genetic predispositions (aptitude) drive individuals to seek out experiences that reinforce those predispositions (appetite).

• Individuals with higher initial ability (genetic endowment) gain environmental advantages, creating a positive feedback loop.

• Conversely, genetic endowment can lead to environmental disadvantages if individuals are predisposed to traits that are not valued or supported in their environment.

Adoption Study Methodology

• Compare child similarity to adoptive vs. biological parents.

• Greater similarity to biological parents suggests genetic influence, as they share genes but not the rearing environment.

• Similarity to adoptive parents suggests environmental influence, as they provide the rearing environment but share no genes.

• Novel designs include adoptions at conception (ART), which allow researchers to study the effects of prenatal environment separate from genetic influences.

Adoption Research

• ART Adoption studies, where children have effectively been adopted at conception, provide unique insights into prenatal and genetic effects.

• Adoption studies where offspring are adopted at birth are powerful for disentangling genetic and environmental effects on development.

Adoption Design Diagram

• BM: Biological Mother

• BF: Biological Father

• AM: Adoptive Mother

• AF: Adoptive Father

• The diagram illustrates the various influences on the child: prenatal effects, genetic inheritance, and rearing environment.

Examples of Adoption Studies

• The Early Growth and Development Study (Leve et al., 2013; Reiss et al., 2022) is a prospective adoption study from birth through middle childhood that examines the interplay of genetic and environmental influences on development.

• Monographs of the Society for Research in Child Development (Reiss, Ganiban, Leve, et al., 2023) focuses on parenting in the context of the child, considering genetic and social processes.

  • $https://doi.org/10.1111/mono.12460$

Evocative Gene-Environment Correlation: Evidence from an Adoption Study (Ge et al., 1996)

• Examined the link between biological parents’ psychiatric history (DSM-III diagnoses) and adoptees' outcomes to investigate evocative rGE.

• Psychiatric disorders considered: antisocial personality disorder, alcohol/drug dependency

• Assessment of family environment, parenting, and child adjustment to determine how parental behavior and family dynamics are related to adoptees' outcomes.

Study Details

• 45 adoptees aged 12-18 years

  • 13 had biological parents with 2+ psychiatric disorders.

  • 15 had biological parents with 1 psychiatric disorder.

  • 17 had biological parents with no disorder.

• Adoptees with biological parents having a psychiatric disorder were defined as genetically at risk, allowing researchers to examine the impact of genetic risk on environmental experiences and outcomes.

Results of the Adoption Study

• Adoptive parents showed more harsh and inconsistent parenting and less warmth toward adolescents whose biological parents had psychiatric disorders (APD, drug/alcohol).

• This indicates that the child evokes negative parenting due to their genetic endowment, supporting the presence of evocative rGE.

• This evocative rGE involved greater hostile behavior from adoptees toward adoptive parents, suggesting a reciprocal relationship between child behavior and parenting.

Mutual Influences (Ge et al., 1996) - Diagram

• The diagram illustrates the complex relationships between biological parents' psychiatric disorders, adoptee's antisocial/hostile behaviors, adoptive parents' disciplinary practices, and marital warmth.

• Displays correlations between various factors: adoptive parents' marital warmth, harsh/inconsistent discipline, nurturant/involved parenting, biological parents' psychiatric disorders.

Inferences from the Adoption Study

• Child-driven effects in parent-child relationships are influenced by the child’s genetic endowment and subsequent behavior, highlighting the importance of considering the child's role in shaping their environment.

• Evidence supports the existence of evocative gene-environment correlation, where children's genetic predispositions elicit certain responses from their environment.

• Parenting influences child behavior, and child behavior also affects parenting in a reciprocal mutual process, emphasizing the dynamic interplay between parent and child.

Mutual Influences of Parenting and Child Behavior (O’Connor et al., 1998)

• Colorado Adoption Project

• Assessment of child adjustment and parenting across ages 7 and 12 to examine the reciprocal relationships between child behavior and parenting over time.

• Child Behavior affected parenting style and vise versa.

• Child aggressive behavior at age 7 predicted the use of negative control as a parenting strategy at age 12 ($r = 0.43$).

• Use of negative control as parenting strategy at age 7 predicted child aggressive behavior at age 12 ($r = 0.39$).

Implications

• Provides evidence of evocative gene-environment correlation, but this did not completely explain effects.

• Evidence for environmental mediation (parental control on children’s behavior) suggests that parenting practices can modify the expression of genetic predispositions.

  • Child effects on parenting may be partly explained by environmental effects, indicating the complexity of parent-child relationships.

• The role of environmental risk cannot be ruled out, as adverse environmental conditions can exacerbate the expression of genetic vulnerabilities.

Gene-Environment Interaction (GxE)

• Genetic endowment may predispose individuals to be susceptible to certain environmental influences, meaning that the effect of a gene depends on the environment, or vice versa.

• Genetic influence on individual susceptibility to particular environments, with some individuals being more sensitive to environmental effects due to their genetic makeup.

• Investigating GxE involves estimating gene and environment contributions to behavior across different environmental circumstances.

• Context can influence the relative contribution of genes and environment, such that the heritability of a trait may be higher in some environments than others.

Potential Value of GxE Research (Zammit and Lewis, 2009)

• Facilitates the identification of novel genetic or non-genetic risk factors for disease, leading to new avenues for prevention and treatment.

• Can increase understanding about disease mechanisms by elucidating the biological pathways through which genes and environment interact to influence disease risk.

• May aid identification of high-risk groups that benefit from targeted interventions, allowing for more efficient and effective use of resources.

Example 1: Depressive Symptoms & Family Conflict (Rice et al., 2006)

• Longitudinal study of 883 twin pairs aged 11-18 years to examine the interplay of family conflict and genetic risk on adolescent depression.

• Family conflict and depressive symptoms were assessed to determine the relationship between these two variables.

• Estimated genetic and environmental contributions to individual differences in depressive symptoms, allowing researchers to partition the variance in depression into genetic and environmental components.

• Allowed estimates to vary by family conflict to investigate whether the heritability of depression differs depending on the level of family conflict.

Family Conflict and Adolescent Depression

• Family history of depression may make children more vulnerable to family conflict, suggesting a gene-environment interaction.

• A stronger effect of family conflict on adolescent depression was seen in individuals at greater genetic risk, providing evidence that genetic risk amplifies the impact of environmental stress.

Example 2: Genes and Child Maltreatment (Caspi et al., 2002)

• Parental maltreatment of children as an environmental risk factor for antisocial behavior.

• Group of males studied from birth to adulthood to examine the long-term effects of maltreatment on antisocial behavior.

• Children with low-activity MAOA genotype (an enzyme) who experienced maltreatment more often developed antisocial behavior and adult violent crime compared to those with a high activity MAOA genotype, indicating a gene-environment interaction where genetic risk moderates the impact of maltreatment.

Example 3: Jaffee et al., (2004)

• Physical maltreatment increases the risk of violent and antisocial behavior (ASB) in adolescence and adulthood.

• Genetic origins: Parents provide the genotype and the rearing environment; maltreatment may form a profile of genetically influenced antisocial behavior (ASB).

• Mothers' reports of child maltreatment (not necessarily by her) and children’s ASB at age 5 and 7 years were analyzed.

Child Antisocial Behavior at 5 and 7 (Jaffee, Caspi, Moffitt, and Taylor)

• Illustrates mean antisocial behavior scores at ages 5 (A) and 7 (B) as a function of physical maltreatment levels.

• Differences between groups are interpreted in terms of standard deviation units (d), with $d = 0.3$ considered a small effect size, $d = 0.5$ a moderate effect size, and $d = 0.8$ a large effect size.

Dose-Response Relationship

• A dose-response relationship was observed between the likelihood of physical maltreatment and ASB at ages 5 and 7.

• Maltreated children had significantly higher levels of later antisocial behavior, indicating a causal relationship between maltreatment and ASB.

• Higher scores on ASB after controlling for initial levels of antisocial behavior indicate that maltreatment independently predicted an increase in adjustment problems.

• While partly accounted for by genetic effects, there remained evidence for environmental mediation: physical maltreatment can be considered a risk factor for ASB.

Implication and Intervention

• Environmental effects mean there is potential to successfully intervene to reduce the risk of ASB and criminality in children exposed to neglectful parenting and physical maltreatment.

• Early interventions are effective and should be used to mitigate the negative impact of maltreatment on children's development.

The MZ Twin Differences Approach

• MZ twins share all their genes, making them genetically identical.

• Differences between MZ twins reared together are attributed to non-shared environmental influence (including measurement error), allowing researchers to isolate the effects of unique environmental experiences.

• The regression approach tests for environmental mediation using an environmental difference score in MZ twins to predict a phenotypic difference score.

Genetically Sensitive Research (Caspi et al., 2004)

• Maternal expressed emotion and child antisocial behavior.

• Study of 565 five-year-old MZ twins (identical) across time to examine the relationship between maternal expressed emotion and child antisocial behavior.

• MZ co-twin exposed to more maternal negativity had more antisocial behavior at age 7, indicating a causal relationship between maternal negativity and child behavior.

Value of These Studies

• Helps us understand why there are individual differences in the long-term effects of abuse and neglect in childhood on adult outcomes.

• Research moves away from partitioning variance based on MZ vs. DZ twins toward increasing specificity of genetic and environmental influence.

• Has policy and practice implications, informing interventions and policies aimed at improving child outcomes.

Genetically Sensitive Animal Research

• Experimental and quasi-experimental studies of 'change' in symptoms in animal studies to investigate the causal effects of genetic and environmental manipulations.

• Suomi (2006) conducted cross-fostering experiments with rhesus monkeys, providing evidence of GxE effects.

• Monkeys carrying the short allele of the 5-HTT gene were more reactive, aggressive, and had higher alcohol consumption as they grew up.

Findings Continued (Animal Research)

• Monkeys with the short allele showed these behaviors only if they were reared with peers only.

• Mother-reared monkeys with the short allele showed species-normative behavior, demonstrating that early rearing environment can buffer genetic risk.

• This has implications for our understanding of individual differences in stress response and adjustment behavior, highlighting the importance of considering both genetic and environmental factors.

Pre-Natal Effects

• Increased interest in prenatal factors, recognizing that the prenatal environment can have long-lasting effects on development.

• Barker hypothesis of early origins of adult disease, which posits that adverse prenatal conditions can increase the risk of chronic diseases in adulthood.

  • Low birth weight, prematurity as indicators of adverse prenatal conditions.

  • Maternal stress/anxiety in pregnancy as a potential source of prenatal stress.

  • Maternal smoking in pregnancy as a modifiable risk factor for adverse prenatal outcomes.

• Difficult to determine whether associations are causal or markers of genetic propensity, as prenatal exposures may be correlated with maternal genes.

Genetically Sensitive Research: Anita Thapar and Colleagues

• A prenatal “cross-fostering design” where mothers are either genetically related or genetically unrelated to their children because of assisted reproductive technologies (ART) to disentangle genetic and environmental contributions to offspring outcomes.

• “Natural experiment” to disentangle inherited and environmental contributions to childhood depression – IVF study.

• Prenatal influences and Inter-generational transmission factors.

Disentangling Inherited and Environmental Contributions

• Using ART allows for the separation of genetic and environmental influences by comparing outcomes in related and unrelated mother-child pairs.

• Genetic and environmental relatives (traditional families) share both genes and environment.

• Genetic relatives (egg donation) share genes but not the prenatal environment with the mother.

• Environmental relatives (surrogacy) share the prenatal environment but not genes with the mother.

Disentangling Genetic and Intrauterine Effects

• IVF Treatment Categories:

  • Homologous (parent’s gametes): Both parents are related, providing a traditional family structure.

  • Sperm donation: Only the mother is related, allowing researchers to examine the effect of maternal genes on offspring outcomes.

  • Egg donation: Only the father is related, allowing researchers to examine the effect of paternal genes on offspring outcomes.

  • Embryo donation: Neither parent is related, providing a unique opportunity to study the effects of the rearing environment in the absence of genetic relatedness.

  • Gestational Surrogacy: Both parents are related, but the child is carried by a surrogate mother, allowing researchers to examine the effect of the prenatal environment on offspring outcomes.

Sample Details for ART Studies

• Families who had a live birth between 1994 and 2002 (children aged 4 to 10 years).

• Families who underwent successful ART treatment using the parents’ gametes (homologous), sperm donation, egg donation, embryo donation, and gestational surrogacy.

• Recruited from 18 UK clinics and 1 USA clinic, total of 888 families.

• Representative of the general population in terms of birth weight, child behavior, and parental characteristics (ART was provided under freely available NHS care in the UK for most of the sample).

Evidence Using This Design

• Prenatal smoking reduced offspring birth weight in both related and unrelated groups, indicating a direct effect of prenatal smoking on birth weight.

• Prenatal mechanism operated independent of the relationship between maternal and offspring genes.

Reference

• Rice, F., Harold, G.T., Boivin, J., Hay, D., van den Bree, M.M.B., Thapar, A (2009). Disentangling prenatal and inherited influences in humans with an experimental design. Proceedings of the National Academy of Sciences USA 106 (7), 2464-2467.

Findings Continued (ART Studies)

• The association between prenatal smoking and offspring antisocial behavior was present only for the related group, suggesting heritable factors account for this relationship.

ADHD and Smoking

• Smoking in pregnancy was associated with lower birth weight in related and unrelated pairs.

• For ADHD symptoms, the magnitude of the association was higher in the related pairs than the unrelated pairs, suggesting a heritable effect.

• Published in Biological Psychiatry (2009).

Conclusion 1

• Genes and environment work together in influencing development, highlighting the importance of considering both genetic and environmental factors in understanding human behavior.

• Genetic endowment may lead individuals to select and construct certain environments compatible with their endowment (gene-environment correlation).

• Genetic endowment may predispose individuals to be susceptible to particular environmental influences (gene-environment interaction).

• The relative contribution of genetic and environmental factors to individual variation in a trait can change according to environmental conditions (context).

Conclusion 2

• Individuals need a functioning complement of genes and an environment in which to exist and develop.

• Environments are DYNAMIC.

  • Children can affect the parenting they receive, but parenting also affects children’s development.

  • Transactions and reciprocal influences are important in shaping developmental outcomes.

  • Individuals play a role in selecting and shaping their environments.

  • As children grow up, become more autonomous, & there are more opportunities for choice, they likely play a more important role in shaping their own environments (e.g., selecting a peer group).

Essential Readings

• Ge X, Conger RD, Cadoret RJ, Neiderhiser JM, Yates W, Troughton E, Stewart MA (1996). The developmental interface between nature and nurture: a mutual influence model of child antisocial behaviour and parent behaviour. Developmental Psychology, 32(4), 574-589.

• Jaffee, S. R., Caspi, A., Moffitt, T. E. & Taylor, A. (2004). Physical Maltreatment Victim to Antisocial Child. Journal of Abnormal Psychology, 113 (1), 44-55. doi: 10.1037/0021-843X.113.1.44.

• Rice, F., Harold, G. T., Shelton, K. H., Thapar, A. (2006). Family conflict interacts with genetic liability in predicting childhood and adolescent depression. Journal of the American Academy of Child and Adolescent Psychiatry. 45, (7), 841-8.

• Rice, F., Harold, G.T., Boivin, J., Hay, D., van den Bree, M.M.B., Thapar, A (2009). Disentangling prenatal and inherited influences in humans with an experimental design. Proceedings of the National Academy of Sciences USA 106 (7), 2464-2467.

• Rutter, M. (2006). Genes and Behavior: Nature and nurture interplay explained. Blackwell: Oxford. ISBN 1-4051-10