Chapter 8 1 BEHAVIORAL GENETICS CHRONIC FATIGUE SYNDROME

Chapter 8 -1 BEHAVIORAL GENETICS

CHRONIC FATIGUE SYNDROME -CFS Symptoms begins as a flu-like illness lasts at least 6 months causes disabling fatigue- bedbound, unable to carry on with routines. Reports of severe physical illness or emotional trauma prior to fatigue. Genetics research study has shown this is real. CFS patients make too little cortisol (stress hormone) make too much serotonin (induces sleep and calms) 2006 - Research found 3 genes – one codes for receptor to bind stress hormones, two affect serotonin levels

BEHAVIORAL TRAITS Includes-feelings, abilities, moods, personality, intelligence, communication, coping with rage and stress. Wide ranging disorders- phobias, anxiety, dementia, psychosis, addiction, mood alteration. Behavior occurs in response to environment but how we respond may have a genetic component. Rarely a single gene Multifactorial Affects 1 in 1, 000. Twin studies & newer –SNP-single nucleotide polymorphism pattern analysis- identify genetic contribution.

BEHAVIORAL GENETICS Study of nervous system and brain variation and function. Brain facts Brain weighs ~ 3 lbs. 100 billion nerve cells (neurons)-do not divide. >1 trillion neuroglial cells- can divide(brain tumors) Produce growth factors Involved in neuron development Neuron movement Brain neurons form synapses with other neurons. Communication occurs via neurotransmitters. Neurons oversee sensations, perceptions, memory, and muscular movement. Genes control production & distribution of the neurotransmitters. Enzymes- oversee synthesis & transport of neurotransmitters across synapse presynaptic (sending) neuron postsynaptic ( receiving) neuron receptors. Transporter proteins ferry neurotransmitters. Review neurotransmission figure.

GENES CONTROL THE SYNTHESIS, LEVELS, AND DISTRIBUTION OF NEUROTRANSMITTERS Figure 8. 1

GENES & MUTATION AFFECTS Myelin- coats and insulates axons (neuron extensions). Speeds neurotransmission. Schizophrenia Signal transduction-series of biochemical reactions , a cascade effect that passes information from outside the cell to inside triggering a response. Mood disorders, mental illness Serotonin Autism. transporter mutation-

DIFFICULTY Hard to identify inherited and environmental contributors to a behavioral disorder. Same symptoms can have different causes. Heritability-estimate (measurement) of the phenotypic variation that is due to genes. observed phenotypic variation /expected. higher heritability %- more genetic influence. What is normal? Range of reactions Subjective reporting bias behaviors can be imitated.

Table 8. 1

INTELLIGENCE Complex and variable trait subject to multiple genes and environmental influences and intense subjectivity Refers to ability to reason, learn, remember, synthesize, deduce, and create. First intelligence tests-sensory & reaction times 1904, IQ(Intelligence quotient) test developed to predict academic success of developmentally handicapped children Stanford University modified for white, middle-class Americans IQ is normally distributed around a mean of 100. below 50 severe mental retardation 50 -70 mild mental retardation 85 -115 average above 115 above average

INTELLIGENCE QUOTIENT (IQ)

HERITABILITY OF INTELLIGENCE CHANGES OVER TIME

IQ CORRELATION Correlates with success-school, work Low IQ-societal situations- poverty, H. S. dropout, high divorce, incarceration, children out of wedlock. IQ tests- short exams Verbal fluency, mathematical reasoning, memory, spatial visualization. g –general or global ability in these 4 areas. Heritability increases with age; environmental effect decreases with age-evens out. Affected by many chromosomal disorders. Gene that encodes for N-CAM ( neural cellular adhesion molecule )– high IQ Chromosome 4 - intelligence related genes.

AUTISM Disorder of communication Asperger syndrome is a related disorder General population incidence < 0. 1% Twin studies – 90% heritability (an estimate of the proportion of phenotypic variation in a group due to genes). 4 – 6 major genes, up to 30 others Autism is probably several different disorders

EATING DISORDERS ARE A BEHAVIORAL TRAIT nervosa psychological perception of obesity and intentional starvation Anorexia psychological perception of obesity and intentional vomiting Bulimia dysmorphia psychological perception of being too small Muscle

GENES AFFECTING EATING DISORDERS genes encode proteins that control appetite, regulate certain neurotransmitters (dopamine and serotonin) SNP maps may identify regions that create a predisposition to eating disorders Candidate

ANOREXIA NERVOSA Women in U. S. have 0. 5% lifetime risk Risk of mortality is 15 -21% 2. 5% risk of second eating disorder 10% of cases are males Heritability of 0. 5 - 0. 8 Concordance 55% MZ twins 7% DZ twins

SLEEPING DISORDERS Without sleep animals die The function remains unclear Genetic contributions are indicated by heritability among families and identification of genes in model systems Twin studies indicate 4 of the 5 stages of sleep have a hereditary component Environmental influence is great

NARCOLEPSY WITH CATAPLEXY • Daytime sleepiness with tendency to rapidly fall asleep (narcolepsy) and periods of muscle weakness (cataplexy) • 1999, first gene identified with sleep in dogs • Problems with receptor for hypocreatin neuropeptide • Orexin protein (signal to eat) binds to receptor

Figure 8. 3

FAMILIAL ADVANCED SLEEP PHASE SYNDROME Heterogeneic, but in this family, the condition is an autosomal dominant caused by a single base substitution Figure 8. 4

DRUG ADDICTION Compulsively seeking and taking a drug despite knowing its adverse effects Characteristics: Tolerance the need to take more of a drug to achieve the same effect Dependence the onset of withdrawal symptoms with cessation of drug

DRUG ADDICTION Brain changes that contribute to addiction are in the limbic system 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 Concordance- measure of degree a trait is inherited by calculating the percentage of twin pairs in which both members express a particular trait. High concordance among identical (MZ) twins indicates a strong genetic component.

Figure 8. 6

PROTEINS INVOLVED IN DRUG ADDICTION Biosynthetic pathways of neurotransmitters Neurotransmitter reuptake transporters Cell surface receptors Signal transduction pathway in postsynaptic neuron

DRUG ADDICTION A candidate gene codes for dopamine D(2) receptor DNA microarray studies reveal many genes whose protein products affect neurotransmission, signal transduction, and myelin deposition on neurons DNA expressions profiles may change with addiction to different drugs

MOOD DISORDERS Mood disorders represent the extremes of normal behavior. Major depressive disorder marked by unexplained lethargy and sadness and chronic depression Bipolar affective disorder (manic-depression) marked by depression interspersed with mania

MOOD DISORDERS Serotonin, a neurotransmitter, can affect mood, emotion, appetite, and sleep Many antidepressive drugs are serotonin reuptake inhibitors (SSRIs)

Figure 8. 7

SCHIZOPHRENIA Loss of ability to organize thoughts and perceptions – withdrawal from reality Worldwide – 1% affected Typically early adult onset Progression – difficulty paying attention, memory and learning difficulties, psychosis (delusions and hallucinations)

SCHIZOPHRENIA IS A MULTIFACTORIAL TRAIT • Empiric risk estimates and heritability (0. 8) indicate a large genetic component • Concordance is high but a person with a schizophrenic MZ twin has a 52% of NOT developing the disease. • Environmental associations important • Many candidate genes and genome regions

ENVIRONMENTAL RISK FACTORS FOR SCHIZOPHRENIA Table 8. 3

REVIEW Table 8. 4