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Genetic and Environmental Influences on Behavior

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The Developmental Psychopathology Perspective. An approach for studying the emergence of behavior disorders that emerged in the past 30 years. Analysis refer to ... – PowerPoint PPT presentation

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Title: Genetic and Environmental Influences on Behavior


1
Genetic and Environmental Influences on
Behavior
  • Chapter 3
  • Theodore P. Beauchaine and Lisa-Gatzke-Kopp

2
HISTORICAL CONTEXT
  • Early causes of psychopathology focused on nature
    versus nurture.
  • Due to lack of formal scientific methods and
    technological and methodological tools it was
    difficult to effectively parse the relative
    contributions of heritable and environmental
    influences on behavior.
  • A growing body of research in the last 10 to 15
    years indicate that Gene Environment
    interactions may be more important in determining
    behavior then either factor alone (Moffitt,
    Caspi, Rutter, 2006 Rutter, 2007).

3
The Developmental Psychopathology Perspective
  • An approach for studying the emergence of
    behavior disorders that emerged in the past 30
    years.
  • Analysis refer to different systems through which
    a psychopathological trait is expressed, spanning
    genes to behavior to broad cultural factors.
  • Integrates the strengths of numerous other
    disciplines, including psychiatric genetics,
    child clinical psychology, child psychiatry,
    developmental psychology, epidemiology, and
    clinical neuroscience.

4
Terminological and Conceptual Issues
  •  Genotypes, Phenotypes, and Endophenotypes
  • Genotype
  • Refers to the structural composition of the
    specific genes within an individual.
  • Some genetic variants give rise to individual
    differences in the synthesis, reuptake, and
    catalysis of neurotransmitters. When functionally
    compromised, these neurotransmitter systems may
    confer vulnerability to mood disorders, impulse
    control problems, and asociality.
  • Both genes and environment are implicated in the
    expression of almost all forms of
    psychopathology.
  • There are no genes for particular behaviors or
    disorders.
  • Environments can alter gene expression.
  • Many people who are genetically vulnerable never
    develop mental illness.

5
Terminological and Conceptual Issues
  • Phenotype
  • Refers to the observable characteristicsboth
    physical and behavioralthat result from the
    interplay between an organisms genes and the
    environment.
  • Most forms of psychopatholoy are polygenetic
    traits and are influenced by many genes.
  • Multiple genetic influences allow for many
    opportunities for both gene-gene interactions and
    environmental regulation of gene expression.

6
Terminological and Conceptual Issues
  • Endophenotype
  • Are a special case of phenotype, as they are
    measurable physical, physiological, or behavioral
    traits the difference is that they are closer to
    the functional output of the gene in question.
  • Endophenotypes are valuable to psychiatric
    geneticists in their attempts to identify
  • Specific alleles associated with psychopathology
  • Genetically vulnerable individuals who have not
    yet developed psychopathology
  • To qualify an endophenotype, a biomarker must
  • Segregate with illness in the general population
  • Be heritable
  • Be state independent
  • Co-segregate with disorder within families
  • Be present at higher rates in affected families
    than in the general population
  • Be measured reliably and specifically

7
Psychiatric Genetics
  • Objectives of psychiatric genetics
  • Behavioral genetics research To parse
    variability in behavioral traits within
    populations into portions accounted for by (a)
    heritable mechanisms, (b) environmental
    mechanisms, and sometimes (c) Gene Environment
    (G E) interactions.
  • Molecular genetics research To identify specific
    alleles that confer vulnerability to
    psychopathology.

8
Psychiatric Genetics
  • Behavioral Genetics
  • Additive Gene Effects
  • Encompass all sources of variance in a behavioral
    trait that are accounted for by heritable
    mechanisms within a population.
  • Maternal programming When genes are activated
    (turned on) among offspring only when their
    mothers are exposed to particular environments,
    often prenatally (Rutter et al., 2006).
  • Such effects may increase risk for or protect
    against the emergence of psychopathology. These
    effects are not purely genetic, yet they are
    often subsumed within the additive genetic
    component in behavioral genetics studies.

9
Psychiatric Genetics
  • Behavioral Genetics
  • Shared and Nonshared Environmental Effects
  • ACE model
  • A is the heritable effects, C is the shared
    environmental effects, and nonshared
    environmental effects are denoted E.
  • When squared, each term signifies a proportion of
    variance in behavior accounted for. In theory,
    these sources sum to 1.0, accounting for all
    variance in a particular trait (A2 C2 E2
    1.0).
  • Research is accomplished through twin, family,
    and adoption studies using the ACE model.

10
Psychiatric Genetics
  • Molecular Genetics
  • Linkage studies Scan broad sections of the
    genome, and require large samples of families
    with two or more children affected by
    psychopathology. Genetic data are collected from
    family members, and searches are conducted for
    genetic markers with known chromosomal locations.
  • Association studies Begin with a specific
    candidate gene that is suspected of conferring
    risk for a psychiatric disorder. Allelic
    frequencies of this gene are then compared among
    those with and without the disorder. Results are
    expressed as odds ratios, which compare the
    likelihood that a person with a candidate
    polymorphism has a target disorder with the
    likelihood that a person without a candidate
    polymorphism has a target disorder.

11
Psychiatric Genetics
  • Heterogeneity of Phenotypes
  • Presents obstacles to identifying genetic
    substrates of psychopathology
  • Criteria used for symptom assessment and
    participant selection often differ across
    studies.
  • Equifinality The same or similar symptoms can
    develop through different etiological pathways.
  • Diagnostic syndromes are highly complex and are
    often defined by a compilation of symptoms.

12
Psychiatric Genetics
  • Gene-Environment Interaction (G E)
  • Refers to situations in which environments
    moderate the effects of genes on behavior, or in
    which genes moderate the effects of environments
    on behavior.
  • Gene-Environment Correlation (rGE)
  • Refers to situations in which heritable traits of
    parents affect their childs exposure to adverse
    environments or heritable traits of children
    affect their own exposure to adverse
    environments.
  • Active rGE occurs when a childs heritable
    vulnerabilities influence his or her selection of
    environments.
  • Evocative rGE occurs when genetically influenced
    behaviors elicit reactions from others that
    interact with and exacerbate existing
    vulnerabilities.
  • Passive rGE occurs when genetic factors that are
    common to both a parent and child influence
    parenting behaviors or home environments more
    generally.

13
Psychiatric Genetics
  • Epigenetics
  • Refers to changes in gene expression that result
    from alterations in DNA structure and are
    mediated primarily by environmentally triggered
    methylation processes (i.e., conversion of a
    cytosine to 5-methylcytosine).
  • Difficult to research epigrnetic changes in gene
    expression humans because it requires random
    assignment of groups to different rearing
    environments (e.g., impoverished versus enriched)
    (Rutter, 2007).
  • Research on the indirect evidence of epigenetic
    processes can be done by measuring methylation of
    target genes.

14
Genetics of Comorbidity
  • Homotypic comorbidity refers to the co-occurrence
    of multiple externalizing disorders within an
    individual or the co-occurrence of multiple
    internalizing disorders within an individual.
  • Heterotypic comorbidity refers to the
    co-occurrence of at least one externalizing
    disorder and at least one internalizing disorder
    within an individual (e.g., CD and depression).

15
Genetics of Comorbidity
  • Behavioral Genetics of Comorbidity
  • Homotypic comorbidity Indicates most disorders
    within the externalizing spectrum share a common
    heritable vulnerability, with similar findings
    reported for disorders within the internalizing
    spectrum.
  • Heterotypic comorbidity Suggest common
    heritability across internalizing and
    externalizing disorders.
  • Molecular Genetics of Comorbidity
  • Homotypic comorbidity Central dopamine (DA)
    dysfunction may account for much of the shared
    vulnerability for externalizing disorders and
    vulnerability for internalizing disorders is
    conferred largely through trait anxiety, which
    has been linked closely with serotonin
    neurotransmission.
  • Heterotypic comorbidity Deficiencies in
    DA-mediated reward circuitry are moderated by
    other biologically influenced traits to affect
    behavior.

16
Genetics of Comorbidity
Symptom overlap for depression and conduct
disorder
17
Genetics of Continuity
  • Homotypic continuity Describes the unfolding of
    a single class of behavioral/emotional
    disturbance over time (e.g., aggression).
  • Heterotypic continuity Refers to the sequential
    development of different internalizing or
    different externalizing behaviors or disorders
    across the lifespan.

18
Conclusions
  • Although boundaries between nature and nurture
    are dissolving, much work remains toward
    uncovering specific mechanisms through which
    nature and nurture interact to affect behavior.
  • Distance between genotypes and phenotypes, along
    with various interdependencies among genotypes,
    phenotypes, and environments, can lead to
    inflated and misleading estimates of
    heritability.
  • Molecular genetics studies aimed at identifying
    specific allelic variations associated with
    psychological dysfunction often fail to account
    for environmental moderators of genetic
    vulnerability.
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