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Transcript
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