Transcript BG Studies of Psychopathology

BG Studies of Psychopathology
• One of the most actively researched areas in recent
years
• It is estimated that 1/3 of the U.S. population suffers
from some kind of mental disorder each year and that
50% will do so at some point in their lives
• Major types of psychopathology that have been
studied include schizophrenia, mood disorders,
anxiety disorders, autism, and ADHD
Schizophrenia
• Long-term mental disorder involving delusions,
hallucinations, and disorganized speech
• Occurs in approximately 1% of the population (= more
than 1,000,000 in the U.S.)
• Typically strikes in late adolescence or early adulthood
• Drug therapy can be successful and has reduced the
number of schizophrenics who require institutional care
BG Studies of Schizophrenia
Risk Estimates for Different Kinships
Kinships
GENERAL POPULATION
FIRST-DEGREE RELATIVES
–
–
–
–
–
PARENTS OF SCHIZOPHRENICS
SIBS OF SCHIZOPHRENICS
DZ TWINS
MZ TWINS
CHILDREN WITH ONE SCHIZOPHRENIC
Percent
1.0
9.0
6.0
9.0
17.0
48.0
12.8
PARENT
–
APOPTED CHILDREN WITH ONE SCHIZO-
11.0
PHRENIC BIOLOGICAL PARENT
–
CHILDREN WITH TWO SCHIZOPHRENIC
PARENTS
SECOND-DEGREE RELATIVES (e.g. grandchildren)
THIRD-DEGREE RELATIVES (e.g. cousins)
ADOPTIVE RELATIVES OF SCHIZOPHRENICS
46.0
4.0
2.4
1.0
Conclusions from BG Studies of
Schizophrenia
• Strong and consistent evidence for genetic influences
• 48% concordance rate among MZ twins means nongenetic factors
are also very important
• When MZ’s discordant for schizophrenia have been studied, there is
some evidence that the schizophrenic twin had birth complications
• Children of discordant MZ twins are equally likely to develop
schizophrenia; among children of discordant DZ twins, those whose
parent was schizophrenic are at much greater risk
• Considerable molecular genetic research has yielded few replicated
results to-date: schizophrenia is likely due to multiple genes each of
small effect
Mood Disorders
• Two major types: unipolar (depression) and bipolar
(depression and mania)
• Major unipolar depression usually has a slow onset (over
weeks or months); each episode may last several months
• Lifetime risk of unipolar depression approximately 17% in
the U.S.; women are twice as much at risk as men after
adolescence
• Bipolar disorder is much less common (approx. 1% of
adults, and no difference between males and females)
BG Studies of Mood Disorders
LESS SEVERE UNIPOLAR DEPRESSION:
• DZ TWINS
• MZ TWINS
RISK
42%
49%
SEVERE UNIPOLAR DEPRESSION:
• POPULATION
• 1ST DEGREE RELATIVES
• DZ TWINS
• MZ TWINS
• RELATIVES OF BIPOLAR
DEPRESSIVES
3%
9%
11%
40%
11%
BIPOLAR DEPRESSION:
• POPULATION
• 1ST DEGREE RELATIVES
• DZ TWINS
• MZ TWINS
• RELATIVES OF UNIPOLAR DEPRESSIVES
1%
8%
40%
72%
1%
Conclusions from BG Studies of Mood Disorders
• Results are less clear-cut than those for schizophrenia,
perhaps because mood disorders are more difficult to
diagnose
• There seems to be some genetic influence on more severe
unipolar depression
• There is clear evidence of genetic influences on bipolar
depression
• Some linkages and gene associations have been reported
but require further replication
Anxiety Disorders
• The most common forms of mental illness: lifetime risk is
approx. 3%
• Typically less severe than schizophrenia or major
depression
• May involve short-term, unexpected panic attacks, or a
more chronic state of generalized anxiety and
uncontrollable worrying
• Other types include phobias (e.g. claustrophobia) and
obsessive compulsive disorder (e.g. anxiety triggered by
inability to perform some compulsive act)
BG Studies of Anxiety Disorders
• Less BG research exists here than on schizophrenia or
depression
• Results are mixed: some twin studies suggest a genetic
influence but others do not
• A recent meta-analysis (Hettema et al., 2001) reported that
panic, generalized anxiety, phobias, and OCD are familial
• Recent multivariate BG studies have also reported a sizeable
(.53) genetic correlation between different anxiety disorders
• Molecular genetic research is scarce and inconclusive
Childhood Mental Disorders
Autism:
– marked by abnormalities in social relationships, delayed
language development, stereotyped/repetitive behaviors
– relatively uncommon: occurs in about 3 to 6 individuals in 10,
000 (0r .03-.06% of the population)
– much more common in boys than girls
Attention-Deficit Hyperactivity Disorder:
– marked by restlessness, poor attention span, impulsive actions
– prevalence rate of approx. 4% of N. American school children
– also much more common in boys than girls
BG Studies of Autism
• Risk to siblings of an autistic child are 3 to 6% (i.e. 100
times more than the population rate)
• Several twin studies suggest a genetic influence: Plomin
estimates a MZ concordance rate of 60% (i.e. 1000 times the
population rate), while DZ concordances are lower
• Initially, autism was thought to be environmentally
determined (cold, rejecting parents) but is now considered
one of the most heritable mental disorders
• Molecular genetic research has yielded some replicated
results: loci on chromosomes 7 and 13 appear implicated
BG Studies of ADHD
• Twin studies have consistently shown strong genetic
influences (h2 = .70)
• Fewer adoption studies exist but also support a genetic
influence
• Considerable molecular genetic research is underway:
several replications showing a linkage between ADHD
and a long-allele polymorphism in the dopamine D4
receptor gene
Multivariate BG Studies of Psychopathology
Key Findings
• No common genetic basis to schizophrenia and bipolar
disorder
• Some evidence that genes predisposing to major
depression also contribute to generalized anxiety
• Other genes appear to co-contribute to phobia, panic
disorder, and bulimia
• As more comorbidity and genetic overlap between
disorders are identified, there are important implications
for clinical diagnostic systems