Personality and Personality
Disorders
Personality
• Personality traits: relatively stable (across
time and situation) individual differences in
behaviour
• Genes make major contributions (~40%)
• Unique environment also important (~60%)
• Shared environment has little effect (but…)
Quantifying Personality
• Huge number of specific tests, models, designs
• Typically self-report questionnaires
– E.g., Myers-Briggs uses 93 forced choice questions,
assuming that the individuals are the best judges of
their own traits
• Traditional theories of personality have put great
value on the shared family environment
– E.g., Freudian analysis, Behaviorism, any nurturist
perspective
Five-Factor Model
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Openness to experience (culture)
Conscientiousness (conformity)
Extraversion (sociability, impulsiveness)
Agreeableness (likeability)
Neuroticism (emotional instability)
Extraversion and neuroticism have received
most behavioural genetics research
Self- vs. Peer Report
• Most use self-reports
• Tends to discount shared environment
• Peer reports generally similar on genes and
unique, but do suggest greater role for
shared environment
Plomin & Caspi (1999)
Percentage of variance
100
80
60
40
20
0
self peer
self peer
Extraversion Neuroticism
Unique environment
self peer
self peer
self peer
Agreeableness Conscientiousness
Openness to
experience
Shared environment
Genetic
Contrast Effects
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Psychometric methodological issue
Correlational studies with twins
Parental assessment
MZ twins typically high
DZ low or sometimes negative
Parents contrast fraternal twins, not
identical
However…
• Lots of personality traits
• Intersection between personality and social
psychology
• Relationships, self-esteem, attitudes
• In some cases, shared environment does
play larger role
Attachment
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Parent-offspring relationship
Strange Situation test
Modest heritability
Substantial shared environment influence
Romantic Relationships
• Waller & Shaver (1994)
– No heritable component to styles/type/aspects of
romantic love (companionship, passion, etc.)
– 0.26 for MZ twins and 0.25 for DZ twins
– Shared environment and unique environment are
determinants
• Text indicates that initial attraction in mate
selection also has no heritable component, but
there are a lot of evolved genetic predispositions
and preferences….
Self-Esteem
• Linked back to depression (low self-esteem
is a core feature of depression)
• Like basic personality traits, moderate
heritability but limited shared environment
effects
Attitudes and Interests
• Specific attitudes and interests are learned
• Hence, will come from shared or unique
environment in the specifics
• However, heritable traits can influence what sorts
of attitudes/interests are acquired
• Consider specific cognitive abilities
– E.g., individual with high mathematical abilities may be
better at chess or poker; reinforced, so plays more
Nature via Nurture
• Traditionalism (conservative vs. liberal
views on wide range of issues)
• Twin and family analysis puts heritability at
about 50% and shared environment at 15%
• Traditionalism could influence religious,
political, sexual, etc. attitudes
Personality Disorders
• Similarities to psychopathology
• Personality traits causing impairment
• Generally viewed by individuals as part of their
“nature” and not a condition to be treated
• Multivariate analysis finds genetic link between
personality disorders and major dimensions of
personality (especially neuroticism)
Personality Disorders
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Schizotypal
Obsessive-compulsive personality
Antisocial
Avoidant
Borderline
Dependent
Histrionic
Narcissistic
Paranoid
Schizoid
Schizotypal Personality Disorder
• Less intense schizophrenia-like symptoms
• Runs in families
– Concordance MZ 33%, DZ 4%
– Higher proportion of 1st degree relative schizotypals of
schizophrenic probands (11%) than controls (2%)
• Danish adoptees:
Schizophrenia
Schizotypal
1st degree biol. rel
5%
24%
Adoptees & controls
0%
3%
Obsessive-Compulsive
Personality Disorder
• OCD compulsion is single sequence of bizarre behaviours
• OCPD involves general preoccupations of trivial details;
interferes with decisions
• No really good twin, adoption, or family studies with
DSM-IV diagnosis
• Twin studies of obsessive symptoms in unselected
population show evidence of moderate heritability
• Substantial overlap with neuroticism
• Obsessive symptoms more common in 1st deg. rel. of
OCD probands (15%) than controls (5%)
Antisocial Personalilty Disorder
• Lying, cheating, stealing; highly variable
– Irresponsibility, irritability, aggressiveness, recklessness, disregard
for truth
• Antisocial personality (ASP)
– Chronic indifference to and violation of rights of others
– Previously often called psychopathy and sociopathy
• DSM-IV: history of illegal or socially disapproved
behaviour, starting before 15 years and continuing into
adulthood, 1% of females, 4% of males (13-40 years)
• Vast majority of juvenile delinquents and children with
conduct disorders do not develop ASP disorder
ASP
• Runs in families
• Adoption studies show genetic, not shared
environment factors
• 1st deg. rel. of male and female probands at
5x and 10x risk, respectively, whether
adopted or not
– Disproportionately male disorder; females need
greater genetic loading
Antisocial Behaviour
• Meta-analysis of 46 twin and adoption studies: shared environment
24%, genetics 40%
• Genetic effects increase with age and shared environmental factors
decrease
• Family members of ASP probands: males at increased risk of ASP &
drug abuse; females for somatization disorders
Crime
• Criminal records are good data sets to work with
• 40% of males & 8% of females with records diagnosed ASP
• Two studies find parents with criminal records have
increased rates of ASP in their adopted away offspring
• Meta-analysis of concordances: MZ 52%, DZ 21%
• 3000 Vietnam War veteran US twins (self-reports) shows
genetics has negligible effect on arrests prior to 15 years;
shared environment has no effect after 15 years
• Adoption studies show less heritability than twin studies
• Some studies find genetic effects on property crime but not
violent crime
• Remember XYY discussion re: general cognition…
Genotype-Environment Interaction
Adopted sons convicted
of criminal offenses (%)
• Alcohol abuse increases probability of
violent crime
Biological parents criminal
25
20
Biological parents not criminal
15
10
5
0
No
Yes
Are adoptive parents criminal?
Identifying Genes for Personality
• Early days
• Novelty seeking and DRD4 (dopamine D4 receptor)
alleleic association
• 7 DRD4 alleles, 2 to 8 repeats of 48 bp sequence
(chromosome 11) codes for dopamine receptor, expressed
in limbic system
• Fewer repeats make protein more effective at binding (in
vitro)
• Within families, long DRD4 --> higher novelty seeking
behaviour
• As if longer repeats make dopamine less effective, so
individual seeks more stimulation to release more
dopamine
DRD4
• Variation in DRD4 explains about 4% of variation in
novelty seeking
• Longer DRD4 repeats also show more hyperactivity and
heroin addiction
• Studies on allelic variation and aggression, shyness, and
neuroticism beginning to turn up significant amounts of
non-additive genetic variance
Neuroticism
• 5-HTTLPR (serotonin transporter gene)
– Linked to neuroticism
– Also linked to schizophrenia, depression
• COMT valine mutation
– Linked to sensation seeking, related to
neuroticism
• Wide ranging neurotransmitter effects
• Conflicting study results re: neuroticism