Transcript PowerPoint

Genetics of
Behavior
The Brain and Behavior
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Genes contribute to
behavioral traits via
effects on the brain
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Remember: genes are
recipes for proteins
Neurons
The Brain: Neurons and Glia
The Synapse
Synapses
Synapses
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Where do things
go wrong?
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Myelin
Neurotransmitter
synthesis
Reuptake
Postsynaptic
receptors
…anywhere
there are
proteins
Behaviors are Often Multifactorial
Traits
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Environment, environment, environment!
Polygenic
Genetic heterogeneity
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Epistasis
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Same collection of symptoms may have different causes
Influenced by temperament and personality
What is “normal”?
Some disorders have various symptoms
Autism
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3 major symptoms, each likely has its own underlying gene
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Impaired communication
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Social problems
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Comfortable only with repetitive behaviors
Incidence is 10-12 per 10,000 (<0.1%)
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Interaction with others is difficult
Rigid repetitive behaviors
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Usually no speech or interaction with others
Higher for siblings (2-4%)
Twin studies indicate 90% heritability
4-5 major genes + 20-30 contributing genes
Eating Disorders
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Anorexia nervosa
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Bulimia
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Person perceives themselves
as obese
Highest risk of death of any
psychiatric disorder (15-20%)
Person binges and purges
90% of eating disorders are in
females
0.5-0.8 heritability
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Little sister may mimic big
sis’s or mom’s eating habits
Christy Henrich 1972-1994
Sleep
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Sleep is “a vital behavior of unknown function”
Strong heritability for sleep characteristics
Narcolepsy
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Individual falls asleep suddenly
Sleep paralysis
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Gene for narcolepsy + cataplexy in dogs discovered in
1999
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Is polygenic in humans
Cataplexy
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Inability to move after awakening
Muscle weakness following excitement
Mutation in the gene for the hypocretin/orexin receptor
Drug Addiction
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Compulsively seeking
and taking a drug despite
knowing its adverse effects
Tolerance
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Dependence
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Need to take more of the drug to have the same effects as
time goes on
Withdrawal symptoms if drug use stopped
Heritability is 0.4 to 0.6
Brain changes occur in the limbic area of the brain
Major Depressive Disorder (MDD)
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Mood disorders may appear to be extremes of
normal behavior
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Many “normal’ people have “highs” and “lows” to some
degree
Lethargy, sadness, no joy from favorite activies
15% of people hospitalized for MDD end their
lives
Partly due to malfunction of the serotonin
transporter
The Neurotransmitter Serotonin
Can
affect mood, emotion, appetite, and sleep
 Many antidepressive drugs are serotonin
reuptake inhibitors (SSRIs)
Bipolar Affective Disorder
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The “effects” of this drug may “affect” my
“affect”
Bouts of depression and bouts of mania
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Manic behavior is reckless and excited
Much less common than MDD
Genetic cause still unknown
Schizophrenia
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Loss of ability to organize thoughts and
perceptions
Delusions and hallucinations
Inappropriate affect
Difficult to pinpoint heritability (~0.8)
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Some symptoms associated with other illnesses
Polygenic
Environmental factors my mimic it (phenocopies)
Genetic Contribution
Environmental Risk Factors
for Schizophrenia
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Deficit subtype
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Associated with summer
births
Negative symptoms
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Lack of emotion
Lack of facial expressions
Non-deficit subtype
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Associated with winter
births
Positive symptoms
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Paranoia
Hallucinations
Delusions
Table 8.3
In Conclusion
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Behavioral traits involve disruption in brain
proteins
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Behavioral traits are multifactorial and often
polygenic