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Human Genetics. Behavioral Genetics. Behavior. Some behaviors can be transmitted from parent to child. What proportion of a behavior results from the action of genes? What proportion of a behavior is learned?

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Human genetics l.jpg

Human Genetics

Behavioral Genetics


Behavior l.jpg
Behavior

  • Some behaviors can be transmitted from parent to child.

  • What proportion of a behavior results from the action of genes?

  • What proportion of a behavior is learned?

  • Behavioral genetics is the study of the genes involved in the development and regulation of the nervous system.


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Genes and Behavior

  • Early 20th century - Extremes of the schools

  • Freud and the psychoanalysis schools

    • all environmental

  • Eugenic movements

    • all bad genes

  • What are the risks of “Blaming Genes”


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How do you define a behavior?

  • need to define the abnormal phenotype

  • need to clearly demarcate it from the "normal"phenotype

  • need to clearly separate it similar "aberrant behaviors“

  •  Alcoholism

    • Phenotype - characteristic deviant behaviors associated with excessive consumption of alcohol

  •  If there is a genetic basis, the phenotype should be mapped to chromosomal markers (RFLP, Microsatellites, SNPs)


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Critical Periods of Development

  • Organs develop at different times in development:

    • A critical period can vary.

  • During its critical period, an organ is vulnerable to toxin, viruses, and genetic abnormalities.

  • Altering the normal development may cause birth defects.


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Tobacco

  • About 20% of women still smoke while they are pregnant

    • twice the rate of premature delivery

    • infants weigh less than normal – < 5 lbs

    • low birth rate is a leading predictor of infant mortality


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Tobacco

  • Nicotine constricts the blood vessels of the placenta

    • less blood flow to the infant

  • Nicotine crosses placenta blood barrier

    • affects brain development

    • impairs cell growth and mental development

  • IUGR - intrauterine growth retardation


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Alcohol

  • Alcoholism affects about 1-2% women of child-bearing age

  • Moderate alcohol during early pregnancy can cause abnormal development

  • Fetal Alcohol syndrome 1-2 per 1000

  • Alcoholics

  • binge drinking episode

  • women - 5 or more drinks in one sitting over 2 or 3 days


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Maternal alcohol abuse is the most common cause of mental retardation

  • Just one drink a day is believed to cause fetal alcohol effects-behavior and learning problems

  • modest drinking in third trimester

  • Decrease in birth weight

  • Constricts placenta blood flow

  • Hypoxia – decrease growth and development


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Fetal Alcohol Effects retardation

  • Greatly increase chance for spontaneous abortion

  • IUGR - intrauterine growth retardation

  • Mental retardation

  • Mimics Autism


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How do we study behavior? retardation

  • Model systems

  • Inbred strains of mice

    • role of vasopressin receptors in prairie voles and mice

    • selectively breed for behaviors


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Gene for Fidelity- in Rodents retardation

  • Single genes can have large behavioral consequences

  • Male mice - quite promiscuous

  • Prairie vole - known for its sociable nature and dedication to one mate

  • What makes their behavior different?


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Why? retardation

  • Scientists have transformed promiscuous male mice into more faithful partners and doting dads by inserting a single gene (vasopressin 1a receptor) from a prairie vole.

  • Hormone vasopressin 1a receptors in the spatial memory region of the vole's brain makes them faithful. If not in that region, the voles are not faithful.


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Most behavioral traits are multifactorial retardation

  • Attention deficit disorder (ADD) or

  • Attention deficit/Hyperactivity disorder (ADHD)

    Siblings of affected child show 3-5x greater risk than those without an affected sibling.

  • Twins studies indicate ~ 80% heritability.

  • Linkage studies indicated dopamine pathway may be involved in ADD/ADHD.


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How do we study behavior? retardation

  • Model systems

  • Drosophila

    • From the fruit fly – we have learned about genes that regulate learning, sexual behavior and motor behavior

    • have been cloned using mutational analysis

    • many of these genes have human homologs


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The brain is composed of neurons. retardation

Transmitting neuron

Receiving neuron

(Presynaptic neuron)

(Postsynaptic neuron)

Axon

Synapse

Direction of action potential



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Cloninger’s Basic Personality Dimensions neurotransmitters.

  • Novelty seeking

  • Avoidance of harm

  • Reward dependence

  • Persistence.

  • Self-directedness (accept yourself)

  • Cooperativeness (accept others)

  • Self-transcendence (feel part of nature)



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Australian Twin Study neurotransmitters.

Earlier Twin Studies showed additive genetic effects accounted for 48% of the variance in Self-transcendence scores for men and women alike.

http://genepi.qimr.edu.au/staff/nick_pdf/CV361.pdf


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The tridimensional personality questionnaire (TPQ) neurotransmitters.

  • Designed to measure aspects of temperament:

    • Novelty Seeking

    • Harm Avoidance

    • Reward Dependence

    • Persistence


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TPQ example Novelty Seeking questions neurotransmitters.

  • True / False

  • I often try new things just for fun or thrills, even if most people think it is a waste of time. (T)

  • I often do things based on how I feel at the moment without thinking about how they were done in the past. (T)

  • I am much more controlled than most people. (F)


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Novelty-Seeking Gene neurotransmitters.

  • Recreational drugs like cocaine, nicotine and alcohol may work through the brain's dopamine system.

  • In Parkinson's disease, the dopamine-producing cells of the brain gradually degenerate. Parkinson’s patients are unusually low in novelty-seeking behavior.

  • The dopamine system has been suggested by Cloninger to play a role in impulsive, extravagant behavior.


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Novelty-Seeking Gene neurotransmitters.

  • High score on the Novelty Seeking scale:

    • impulsive, exploratory, fickle, excitable, quick-tempered, extravagant

  • Low score on the Novelty Seeking scale:

    • reflective, rigid, loyal, stoic, slow-tempered, frugal


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Novelty-Seeking Gene neurotransmitters.

  • Dopamine D4 receptor (D4DR) exon III polymorphism associated with the human personality trait of Novelty Seeking.

  • Richard Ebstein et al., 1996

  • Population and familial association between the D4 dopamine receptor gene and measures of Novelty Seeking.

  • Jonathan Benjamin, et al., 1996

  • Dean Hamer lab, NIH


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Novelty-Seeking Gene neurotransmitters.

  • Studies have shown that the number of exon III repeats can affect the affinity of ligand (proteins or drugs) that bind to the receptor.

  • D4DR is expressed in limbic areas involved in cognition and emotion.


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Novelty-Seeking Gene neurotransmitters.

  • Research on animals, as well as extensive studies of human twins of both the identical and fraternal variety, indicate that about half of novelty-seeking behavior is attributable to genes, the other half to as-yet ill-defined environmental circumstances.

  • The D4 dopamine receptor may account for perhaps 10 % of the difference in novelty-seeking behavior between persons.


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Novelty-Seeking Gene neurotransmitters.

  • Some studies have failed to replicate the initial findings.

  • The Dopamine D4 Receptor Gene and Novelty Seeking

  • Anil K. Malhorta, M.D., and David Goldman, M.D.

  • Finnish Population


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Novelty-Seeking Gene neurotransmitters.

  • Were the early results just due to chance results in small or unusual populations, and not a real effect of D4DR, or not representative of the general population?

  • Further evidence for a modulation of Novelty Seeking by DRD4 exon III, 5-HTTLPR and COMT val/met variants.

  • A. Strobel et al. 2003

    • (Same group as prior report)


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Novelty-Seeking Gene neurotransmitters.

  • Benjamin et al. had found:

    • Novelty Seeking scores are higher in the presence of the DRD4 exon III 7-repeat allele in the absence of the short (s) allele of the serotonin transporter gene promoter-linked polymorphic region (5-HTTLPR) and in the presence of the val/met genotype of the COMT gene.


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Novelty-Seeking Gene neurotransmitters.

  • Benjamin suggested "that failure to replicate associations between personality factors and some genes may be partially due to the presence of additional modifying common polymorphisms".


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Novelty-Seeking Gene neurotransmitters.

  • Strobel et al. decided to see if this effect explained their failure to find an association in their German population.

  • Genotyped 5-HTTLPR and COMT val/met in their prior subjects.


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Hypothesis neurotransmitters.

  • In the group defined by 5-HTTLPR 1/1 genotype and COMT val/val genotype, individuals with the DRD4 exon III 7-repeat allele would have higher Novelty Seeking scores than those without the repeat.


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Results neurotransmitters.

  • Found a significant difference between those with and without the 7-repeat allele, p = 0.035 after accounting for differences in the other polymorphisms.

  • The study shows that the failure to detect an effect (due to D4DR polymorphisms) could be explained by the presence of additional modifying common polymorphisms.

  • Inclusion of additional genetic variations may help resolve some of the inconsistencies in human gene-personality/behavior correlation studies.

  • http://www.nature.com/mp/journal/v8/n10/pdf/4001367a.pdf

  • Review Article of many studies


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Criminal Behavior/Violence neurotransmitters.

  • Classic nature versus nurture arguments

  • 1993 study of a Dutch family describes one long family history of " a syndrome of borderline mental retardation and abnormal behavior"


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Co-segregation of mental retardation, aggressive behavior and a mutation in monoamine oxidase type A gene (MAOA).

* - males known to have the mutated MAOA allele.

Δ - males known to have the normal MAOA allele


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Monoamine oxidase type A gene and a mutation in monoamine oxidase type A gene (MAOA).

  • Familial defect?

    • Single nucleotide substitution in the enzyme monoamine oxidase A (MAOA)

    • renders the enzyme non-functional

  • MAOA is a key enzyme

    • required to breakdown several neurotransmitters

    • dopamine, serotonin and noradrenaline.

    • behavioral defects not unexpected

  • What if one inherits a slight mental impairment that interferes with a persons ability to cope with frustrating situations -resulting in violence?


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Genetic and Environmental Effects and a mutation in monoamine oxidase type A gene (MAOA).

  • Role of Genotype in the Cycle of Violence in Maltreated Children

  • Avshalom Caspi et al. 2002

  • wanted to identify gene variants that, given specific environmental triggers, predispose individuals to anti-social behavior

  • Low MAOA activity in abused boys led to criminal behavior

  • Low MAOA by itself was normal

  • High MAOA in abused boys had less criminal behavior observed, but more than unabused.


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Genetic control of human behavior and a mutation in monoamine oxidase type A gene (MAOA).

  • Supported by pedigree analysis

  • Family studies

  • Twin and adoption studies

  • Identification of susceptibility genes

  • Identification of single gene mutations

  • Most behaviors are complex

  • Many genes contribute to the expression of the trait

  • Behavioral traits are not easily measured

  • Subjective rather than objective measurements


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If Personality Runs in Families, so too does Mental Illness and a mutation in monoamine oxidase type A gene (MAOA).

  • Prior to 1966, schizophrenia was thought to be related to environmental conditions and poor parenting

  • 1966 - key study showed Infants put up for adoption by schizophrenic mothers showed the same rate of schizophrenia expected for being raised by a schizophrenic mother


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Disease Prevalence % and a mutation in monoamine oxidase type A gene (MAOA).

Alzheimer disease 4.0

Anxiety 8.0

Phobias 2.5

Post-traumatic stress disorder 1.8

Generalized anxiety disorder 1.5

Obsessive compulsive disorder 1.2

Panic disorder 1.0

Attention deficit hyperactivity disorder 2.0

Autism 0.1

Drug addiction 4.0

Eating disorders 3.0

Mood disorders 7.0

Major depression 6.0

Bipolar disorder 1.0

Schizophrenia 1.3


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Single Gene Mutations and Abnormal Behavior and a mutation in monoamine oxidase type A gene (MAOA).

  • PKU: phenylketonuria

    • Leads to severe metal retardation

    • Single gene defect - major behavioral mutation

    • Avoid Phenylalanine in diet- screening for infants to detect

  • Lesch-Nyhan Syndrome

    • X-linked recessive trait

    • affects 1 in 100,000 males

    • inborn error of metabolism

    • lack the enzyme hypoxanthine-guanine phosphoribosyltransferase 

    • High level of uric acid in the blood and urine

    • Strong tendency for self-mutilation

    • Symptoms fully develop by ages 2-4

    • Most die before age 20


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Huntington's Disease and a mutation in monoamine oxidase type A gene (MAOA).

  • Autosomal dominant disease

    • Late onset - mid-adult

  • First observed characteristic

    • Involuntary muscle movements of arms, legs, torso

  • Later - personality changes, agitated behavior and dementia

  • Associated with expanding CAG triplet repeats

  • Disease runs a 10-15 yr course of progressively worsening condition

  • Autopsy show severe loss of brain areas

  • Gene product - Huntingtin

  • House keeping neuron protein


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Normal brain Huntington’s diseased brain and a mutation in monoamine oxidase type A gene (MAOA).


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Relationships of genetic defects and abnormal behavior and a mutation in monoamine oxidase type A gene (MAOA).

  • PKU and Lesch-Nyhan

    • build up toxic chemicals that neurons are very sensitive to.

  • Huntington's

    • slow progressive death of neurons

  •  MAOA

    • aggressive behavior gene

    • a single gene mutation

    • an inborn error of metabolism

    • persons are basically functional - but have improper control of behavior when stressed by fear, anger, frustration


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Eating disorders are a behavioral trait and a mutation in monoamine oxidase type A gene (MAOA).

  • Anorexia nervosa

    • psychological perception of obesity and intentional starvation

  • Bulimia

    • psychological perception of obesity and intentional vomiting

  • Muscle dysmorphia

    • results from steroid consumption to develop enlarged musculature


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Anorexia nervosa and a mutation in monoamine oxidase type A gene (MAOA).

  • Women in U.S. have 5% lifetime risk

  • Risk of mortality due to anorexia is 15-21%.

  • Individuals with anorexia nervosa have 2.5% risk of second eating disorder.

  • 10% of cases are males.

  • Heritability of 0.5 - 0.8

    e.g. 9/16 MZ twins concordant versus 1/14 DZ twins

  • No causal genes have been identified to date.


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Sleep Disorders and a mutation in monoamine oxidase type A gene (MAOA).

  • Without sleep animals die. The function of sleep remains unclear.

  • Genetic contributions are indicated by heritability among families and identification of genes in model systems.

  • Environment influence is great. Sleep-wake cycles are regulated in part by light via the suprachiasmatic nucleus in the brain.


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Narcolepsy with cataplexy and a mutation in monoamine oxidase type A gene (MAOA).

  • Daytime sleepiness with tendency to rapidly fall asleep (narcolepsy) and periods of muscle weakness (cataplexy)

  • Genetic contribution is indicated:

    • 0.02-0.06% general population in US and Europe

    • 1-2% risk with first degree relative

    • 25-31% concordance among MZ twins

  • Model of narcolepsy in dogs:

    • Fully penetrant autosomal recessive trait due to allele at gene canarc-1.

    • http://www.youtube.com/watch?v=NSKO39HIkAo


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Familial advanced sleep phase syndrome and a mutation in monoamine oxidase type A gene (MAOA).


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  • Drug addiction produces stable, not transient, changes in the brain

    • Heritability is 0.4-0.6

  • Twin and adoption studies support role of genes in drug addiction.

  • Tolerance

    • the need to take more of a drug to achieve the same effect

  • Dependence

    • the onset of withdrawal symptoms with cessation of drug


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Mood Disorders the brain

  • Moods are defined as sustained emotions

  • Affect – short term expression of emotion

  • Affective disorders (mood disorders)

    • Behavioral disorders associated with manic and/or depressive syndromes

  • Two basic classes of affective disorders

    • unipolar – periods of prolonged depression

    • bipolar - cycles of depression that alternate with periods of elation


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Mood Disorders the brain

  • Life time risk of a clinically identifiable affective disorder is 8-9%

  • 1 out of 10

  • Depression is the most common (unipolar disorder)

    • More common in females than males (2:1)

    • Often begins in your 40-50s

    • Often recurrent and protracted

    •  weight loss, insomnia, poor concentration, irritability, anxiety and lack of interest of surrounding events


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What is the evidence that mood disorders have a genetic component?

  • Twin studies

    • 57% concordance for MZ

    • 14% concordance in for DZ

  • Attempts to map the genes have been generally unsuccessful

    • Failure to find linkage

    • Novel techniques are being used to map these genes


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Bipolar Disorders component?

  • About 1% of the US population suffers from bipolar disorders

    • Age of onset can be as early as adolescence, often occurs in 20s and 30s

    • Males and females similar

  • hyperactivity, acceleration of thought process, low attention span, creativity and feelings of elation and power

  • Many manic depressives are highly creative people

    • “thin line that separates genius and madness”

  • manic depressive have unique patterns of metabolism and blood flow in the prefrontal cortex-a part of the brain associated with intellect


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Bipolar Disorder Spectrum component?

  • Symptoms include dramatic moods swings between euphoria and severe depression; patients may have hallucinations or delusions.

    • Bipolar disorder I More severe symptoms

    • Bipolar disorder II. Less severe symptoms

  • Study researchers say health professionals should recognize a third and milder category --sub-threshold bipolar disorder.

  • In 2006, NIMH researcher Kathleen Merikangas estimated 2.6% of the U.S. population (5.7 million American adults) suffered from bipolar disorder in any given year.

Lifetime and 12-Month Prevalence of Bipolar Spectrum Disorder in the National Comorbidity Survey Replication. Merikangas, KR et al. Arch Gen Psychiatry. 2007;64(5):543-552.


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Bipolar Disorder Spectrum component?

  • BPD is a leading cause of premature mortality due to suicide and associated medical conditions, such as diabetes mellitus and cardiovascular disease.

  • Researchers discovered many patients were in treatment but not getting the correct medications.

  • 80% of cases begin between the ages of 18 and 24 years.

  • Increasing number of childhood bipolar diagnoses

    • http://www.nytimes.com/2008/09/14/magazine/14bipolar-t.html?pagewanted=1&em


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Bipolar Disorder Spectrum component?

  • When patients who met the diagnostic criteria for sub-threshold bipolar disorder were included, Merikangas and NIMH colleagues concluded 4.4% of U.S. adults have some degree of bipolar illness during some point in their lives.

  • The lifetime incidence of bipolar I and bipolar II was roughly 1% each in the surveyed population and 2.4% for sub-threshold bipolar disorder.

  • "The [findings] reinforce the argument of other researchers that clinically significant sub-threshold bipolar disorder is at least as common as threshold bipolar disorder," Merikangas and colleagues wrote in the May issue of Archives of General Psychiatry.


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Inheritance of Bipolar Disorder component?

  • Diagnostic criteria for bipolar affective disorder define a phenotype that is highly heritable, yet clinically variable.

  • A better definition could improve genetic and other studies, but the best approach is unclear.

  • Variable occurrence of psychosis, suicidality, and rapid cycling among people with the bipolar I subtype.

  • The clinical variability may reflect underlying heterogeneity at the biological and genetic levels.

What Is Familial About Familial Bipolar Disorder? Schulze, TG et al. Arch Gen Psychiatry. 2006;63:1368-1376.


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Inheritance of Bipolar Disorder component?

  • Gene-mapping benefits from an approach that seeks to decrease clinical variability among cases while maintaining the high heritability that makes BP a good target for gene mapping efforts. This is referred to as "refining the phenotype.“

  • Is BP caused by many genes of small heritability, or is it actually more than one syndrome, caused by different genes which cause similar symptoms?

What Is Familial About Familial Bipolar Disorder? Schulze, TG et al. Arch Gen Psychiatry. 2006;63:1368-1376.


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Inheritance of Bipolar Disorder component?

  • Family studies indicated definitions of the affected phenotype of BPAD might usefully consider co-morbid conditions and social functioning along with traditional symptoms.

  • “People whose bipolar disorder is complicated by substance abuse, psychosis, and poor social relations may well differ genetically from those whose illness shows none of these features.”

What Is Familial About Familial Bipolar Disorder? Schulze, TG et al. Arch Gen Psychiatry. 2006;63:1368-1376.


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Columbia Bipolar Genetic Study component?

  • In 1986, the Columbia Bipolar Genetic Study began studying generations of families with bipolar illness.

  • Goal is to search for bipolar disease genes will lead to improved diagnosis, treatment, early intervention, and prevention of bipolar illness.

http://bipolar.hs.columbia.edu/identify.htm


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How are genes identified? component?

  • Locate research participants

    • Locate and interview a large number of families that have a significant number of members with the illness.

    • Confirm key family members' history through phone interviews and available medical records.

  • Collect blood samples

    • Extract DNA - the genetic material - from the blood cells

http://bipolar.hs.columbia.edu/identify.htm


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How are genes identified? component?

  • Scan the DNA

    • Genetic markers are variations in the DNA that are used for identification purposes. For the most part, they occur naturally and have no causative role. Scientists use genetic markers to locate genes, just as travelers use landmarks to locate destinations. Genetic markers are often referred to as "signposts" along the DNA.

    • The DNA is scanned in the laboratory for linkage between the markers and the occurrence of the disorder.

http://bipolar.hs.columbia.edu/identify.htm


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How are genes identified? component?

  • Establish Linkage

    • Linkage refers to a a statistical association between a genetic marker and the occurrence of bipolar disorder within a family or families.

    • If linkage is established, specialized molecular genetic techniques are used to isolate the gene itself. Multiple steps are involved to narrow the search for the gene or genes involved.

http://bipolar.hs.columbia.edu/identify.htm


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How are genes identified? component?

  • Analyze the gene

    • Determine its DNA sequence.

    • Compare the gene from an individual with bipolar disorder with the same gene from an unaffected individual. Look for sequence differences in the gene that could be helpful in diagnosis.

    • Identify the gene's "product" to learn how it affects the brain. For example, the gene might produce an enzyme or neurotransmitter that affects brain function.

    • Once the gene's "product" is identified, and its relationship to bipolar disorder is understood, treatment can be developed

http://bipolar.hs.columbia.edu/identify.htm


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Mechanism of Drug Action component?for SRI


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Mood disorders component?

  • Serotonin, a neurotransmitter, can affect mood, emotion, appetite and sleep

  • Many antidepressive drugs are serotonin reuptake inhibitors (SSRIs) including Prozac, Paxil and Zoloft.


Schizophrenia l.jpg
Schizophrenia component?

  • A disorder marked by the loss of the ability to organize thoughts and perceptions leading to withdrawal from reality.

  • Affects 1% of worldwide population.

  • Progression of disorder:

    • Difficulty paying attention

    • Memory and learning skills affected

    • Psychosis (17-27 males, 20-37 females) delusions and hallucinations

  • up to 50% of all hospitalized, mentally ill and mentally retarded individuals are schizophrenic


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Two models of Schizophrenia component?

  • Genetics primary and environment secondary

  • Environment primary and genetic secondary

  • There appears to be a genetic basis, but environmental inputs necessary for full expression


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Risk Factors for Schizophrenia component?

  • You have a 15% lifetime risk of developing schizophrenia if a relative has schizophrenia compared to 1% among unrelated individuals.

  • Environmental Risk Factors

    • Maternal malnutrition

    • Infection by Borna virus

    • Fetal oxygen deprivation

    • Obstetric or birth complication

    • Psychoactive drug use (PCP)

    • Traumatic brain injury

    • Herpes infection at time of birth



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Tourette syndrome component?

  •  Motor and behavioral disorder

  • Hard to follow it inheritance

  • About 10% of patients have a family history

  • 33:1 males

  • Onset is between 2 and 14 years of age


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Alzheimer Disease component?

  • Loss of memory with progressive dementia

  • Development of brain lesions

    • Occurs in about 10% of the population over age 50

    • Occurs in about 50% of those over age 80

  • senile plaques

    • composed of amyloid beta-protein

  • Alzheimer patients - accumulate plaques faster and in greater numbers

  • both genetic components and environmental components have been identified


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Types of inherited Alzheimer Disease (AD) component?

  • AD1 -early onset Alzheimer (AD1)

    • mutations in amyloid beta-protein gene(C21)

    • autosomal dominant

  • AD2 - associated with allele APOE*4 (C19)

  • AD3 - mutation in a membrane protein (C14)

    • Hannah – 1880

    • 1974 Hannah’s grandson and great-grandson, constructed a family pedigree

    • 1992 gene was cloned

    • presenilin 1

    • receptor located in the golgi membrane

  • AD4 - mutation in a membrane bound protein (C1)


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Environmental factors component?

  • aluminum

    • often found in the amyloid deposits

  • Prion-like molecules

    • Prions are proteins that cause several types of disorders

    • often neurodegenerative

    • best known - mad cow disease



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Is homosexuality inherited? component?

  • 1980, American Psychiatric Association removed homosexuality as a disease. Reclassified as a simple variant form of human behavior

  • Pooling data from several studies using twins

    • 57% of MZ twin brothers of gay men are themselves gay

    • 24% of DZ twin brothers of gay men are themselves gay

    • 50% of MZ twin sisters of gay women are themselves gay

    • 16% of DZ twin sisters of gay women are themselves gay


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Is homosexuality inherited? component?

  • Repeatedly show that homosexuality clusters in families

  • Pedigrees indicated a much higher rate of gay brothers, uncles and male cousins in these families than expected for the general population

  • Most apparent gay inheritance follows maternal lines rather than paternal lines

  • Suggests that genes regulating sexual orientation are present on the X chromosome


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Is homosexuality inherited? component?

  • X-linked inheritance is supported by inheritance of DNA markers

  • 33 out of 40 pairs of gay brothers all have exactly the same 5 alleles of five nearby markers on the X chromosome

  • heterosexual brothers of the same families do not have the same full set of all five alleles


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Intelligence component?

  • http://www.sciam.com/article.cfm?id=searching-for-intelligence-in-our-genes


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Summary: Genes and behavior component?

  • Some abnormal behaviors have been traced to single gene mutations

  • Most are complex multifactorial traits

    • There is great difficulty in defining a behavioral phenotype

    • Complex environmental components

  • Basic issues in defining an abnormal behavior phenotype

    • It is subjective

  • We have to discriminate between the normal variants and what is truly abnormal

    • Quiet, shy people vs boisterous, aggressive individuals

  • Culture is a major player - society defines the norms


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