Michael Mao
Honors Seminar: Genes and Behavior
March 31, 2004
Summary for Genes and Disorder Presentation
Girls, Boys, and Autism
This article in Newsweek magazine describes children with autism and the traits that they
often exhibit in comparison to normal children. The article begins by showing that the psychologist
Simon Baron-Cohen has connected autism as an imbalance between two kinds of human
intelligence, which are designated as “empathizing” intelligence and “systemizing” intelligence.
Empathizing intelligence is the intelligence that females are usually stronger at, and deals with
understanding people and being proficient in social conditions. Systemizing is the kind of
intelligence dealing with understanding facts, rule-based systems, and classifying information.
Autistic individuals are thus defined as individuals that are individuals that are “more male than the
men,” hence possessing a large imbalance favoring the systemizing intelligence. The article
continues by noting that autism has changed from the classical definition as a devastating
neurological disorder to a condition that can affect people differently and to different degrees,
giving both mentally retarded and gifted individuals. Studies have further shown that rapid brain
growth during early childhood is associated with this disorder.
The traits of autism usually consist of leaving individuals devoid of social impulses and the
ability to communicate with others. However, autistic individuals are also infamous for their ability
to recall a vast amount of facts with incredible precision and speed. For example, the article
compares the drawing of normal children that often reflect childhood interests such as houses and
robots to an autistic child’s drawing of a train that is amazingly detailed, complete with proper
perspective. Yet these same children are often unresponsive to social conversations and find people
unpredictable. Studies have shown that treatment through electronic flashcards displaying an
emotion to corresponding human expression may aid in treating certain affects of autism.
Nature and Nurture and Psychology: Genetics of Reading Disability
I.
Reading Disability: Other terms found in literature include specific reading disability,
specific developmental dyslexia, and unexpected reading failure.
a. This system is when an individual develops in every area normally except that the
individual is unable to read.
b. Family studies have confirmed a familial nature of reading disability.
c. Twin study has given evidence that reading disability is caused at least partly to
heritable influences.
II.
Genetic Linkage Analyses
a. Genes located near each other on the same chromosome tend to be transmitted
together while chromosomes located further apart or on different chromosomes are
inherited independently.
i. This allows genes to be mapped or localized to a specific chromosomal
region by comparing its transmission pattern to known marker genes.
ii. Evidence of linkage is found by computing the LOD score.
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1. Quantification of linkage between gene of interest and marker.
2. Acronym for the logarithm to the base 10 of the odds.
3. Odds= conditional probability of observing cotransmission between
the character and a marker, given linkage, divided by the probability
of cotransmission, given independent assortment.
b. Studies from 84 individuals that were members of nine extended families possessing
reading disability showed that it was transmitted in autosomal dominant manner.
i. Furthermore, there was a total LOD score of 3.2 for the marker on
chromosome 15. Later reduced to 1.33 with extended study.
ii. Results suggest that the condition is genetically heterogeneous.
iii. Indication that most cases of heritable reading disability must be caused by
genes at other chromosomal locations.
c. Linkage analysis of complex characters with extended family pedigrees is severely
limited.
i. Several chromosomal locations can possibly influence traits.
ii. Each individual must be accurately diagnosed across a wide age range and
through generations.
iii. Sibling-pair analysis, though less powerful, can also be used.
1. Use of the “identical by descent” (IBD), parents must also be
genotyped.
2. Possible linkage found between chromosomes 6 and 15.
d. Haseman and Elston approach is a modification of the sibling-pair analysis.
i. Conceptually simpler.
ii. Can be applied using computer programs.
iii. Applicable for data from selected or unselected samples
iv. Highly flexible. Allows analysis of variables such as age and gender.
v. Statistically powerful, especially for selected samples.
III.
Concluding Remarks
a. The use of molecular genetics will revolutionize the field of behavioral genetics.
This can be demonstrated through the use of restriction fragment-length
polymorphisms (RFLPs) to find Huntington’s disease.
b. Another technique in genetic mapping involves the use of polymorphisms in
microsatellite sequences.
c. Polymerase chain reaction to amplify DNA will also assist future gene mapping.
d. Single-Gene and quantitative genetic analyses are complementary.
Packet on Dyslexia, Anorexia Nervosa, and Schizophrenia
I.
Dyslexia
a. Causes difficulty in recognizing and reading words.
b. Process information in different area of brain: use right side for reading instead of
the left side.
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c. A single gene called DYXC1 may cause the condition. Found through family
studies.
i. DYXC1 may help cells cope with stress.
ii. Other genes may cause dyslexia.
iii. If this candidate gene is indeed responsible, could allow children to be
diagnosed early and treated with drugs.
II.
Anorexia nervosa (restrictive subtype)
a. Anorexia nervosa (AN) has been associated with lower norepinephrine levels, caused
possibly by a polymorphism in the novel norepinephrine transporter gene promoter
polymorphic region.
i. AN-R associated with L4.
ii. Significant difference in allelic transmission to AN-R and AN-BP patients.
iii. Preferential transmission of different alleles to AN-R and AN-BP suggest
association of AN-R with l4 is not cause by segregation distortion.
iv. The polymorphic region in the 5’ promoter region of the NET gene is
designated as the NETpPR. A positive polymorphism in their region
produced a positive association with AN-R.
b. Anorexia nervosa associated with anxiety disorders.
i. Evidence suggests noradrenergic brain systems are involved.
ii. Since NET regulates norepinephrine, it also has a role in anxiety of AN.
c. Atypical AN may respond to venlafaxine.
III.
Schizophrenia
a. No one is born with schizophrenia.
i. Develops ambiguously: sometimes slow and mysteriously, other times
abruptly.
ii. Most cases appear around 15 to 35 years old.
iii. Males and females equally affected.
iv. Prognosis.
1. High risk of death from suicide.
2. May require extensive mental health assistance after illness.
3. Affects cognition, attention, affect, motivation, personality, and motor
behavior.
4. No single symptom is found in all schizophrenics.
b. No biological marker to diagnose schizophrenia.
i. Within the schizophrenic brain, the ventricles are larger on average than
normal brains, though it cannot be used as a diagnostic measure.
ii. Some experts suspect that schizophrenia is a composed of many
heterogeneous disorders.
iii. Schizophrenics tend to be abnormal in terms of anything related to the
nervous system, cognitive trait, personality, social interaction, or any other
human affect.
iv. Causes and consequences of schizophrenia are difficult to discern.
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c. Genetic Epidemiology of Schizophrenia I: Heritability
i. Data shows that schizophrenia is not a simple, fully penetrant recessive or
dominant disorder.
ii. Data implies that more than 90% of schizophrenics will be born to
nonschizophrenic parents.
iii. Genes play an important role in familial aggregation of schizophrenia.
iv. Biological relatives, not adoptive relatives, predict schizophrenia in adoptees.
v. No knowledge of the mode of transmission of schizophrenia currently.
d. Genetic Epidemiology of Schizophrenia II: Beyond Heritability
i. MZ twins have similar ages of onset, clinical signs and symptoms, and
courses of illness.
1. Supports the hypothesis that schizophrenia is a heterogeneous
collection of disorders.
2. Genes might be involved in influencing the form of schizophrenia
instead of contributing to it.
e. Schizotypal personality disorder (SPD) is a phenomenon where first-degree relatives
exhibit the same symptoms of full-blown schizophrenics but are less severe.
i. Data suggests SPD is familial and genetically related to complete
schizophrenia.
ii. Severity of schizophrenia in proband is associated with familial risks
(severity-concordance relationship).
1. Caused by marked heterogeneity in schizophrenia. Less severe cases
may contain more phenocopies than more severe cases.
2. Due to multifactorial, polygenic transmission, the more severe cases
contain more genetic “loading” than mild cases.
3. Variances caused by difficulties in diagnosis.
iii. Association between laterality and discordance found through MZ twins.
iv. Personality aberrations and unusual cognitive functioning may be
consequences of the disease.
v. Ill twins tend to have larger brain ventricles, more EEG abnormalities,
auditory information processing, and neurological soft signs than normal
twins.
vi. Data supports that both normal and ill twins would have the same, elevated
risk of developing schizophrenia.
IV.
Other Forms of Psychopathology
a. In other disorders, results have been similar in these ways:
i. MZ twins are never completely concordant for a disorder. Thus
environmental factors are always present.
ii. Risks to relatives do not follow simple Mendelian genetic inheritance.
iii. Despite suspected heterogeneity, no subdivision of any disorder into “types”
has been definitely ascertained.
iv. No genes of immense effect have been reported by a large and replicated
body of linkage or association results.