| 1. |
- Lewis, Cathryn M, et al.
(författare)
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Genome scan meta-analysis of schizophrenia and bipolar disorder, part II : Schizophrenia
- 2003
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Ingår i: American Journal of Human Genetics. - 0002-9297 .- 1537-6605. ; 73:1, s. 34-48
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Tidskriftsartikel (refereegranskat)abstract
- Schizophrenia is a common disorder with high heritability and a 10-fold increase in risk to siblings of probands. Replication has been inconsistent for reports of significant genetic linkage. To assess evidence for linkage across studies, rank-based genome scan meta-analysis (GSMA) was applied to data from 20 schizophrenia genome scans. Each marker for each scan was assigned to 1 of 120 30-cM bins, with the bins ranked by linkage scores (1 = most significant) and the ranks averaged across studies (R(avg)) and then weighted for sample size (N(sqrt)[affected casess]). A permutation test was used to compute the probability of observing, by chance, each bin's average rank (P(AvgRnk)) or of observing it for a bin with the same place (first, second, etc.) in the order of average ranks in each permutation (P(ord)). The GSMA produced significant genomewide evidence for linkage on chromosome 2q (PAvgRnk<.000417). Two aggregate criteria for linkage were also met (clusters of nominally significant P values that did not occur in 1,000 replicates of the entire data set with no linkage present): 12 consecutive bins with both P(AvgRnk) and P(ord)<.05, including regions of chromosomes 5q, 3p, 11q, 6p, 1q, 22q, 8p, 20q, and 14p, and 19 consecutive bins with P(ord)<.05, additionally including regions of chromosomes 16q, 18q, 10p, 15q, 6q, and 17q. There is greater consistency of linkage results across studies than has been previously recognized. The results suggest that some or all of these regions contain loci that increase susceptibility to schizophrenia in diverse populations.
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| 2. |
- Hettema, John M, et al.
(författare)
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A twin study of the genetics of fear conditioning.
- 2003
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Ingår i: Arch Gen Psychiatry. - : American Medical Association (AMA). - 0003-990X. ; 60:7, s. 702-8
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Tidskriftsartikel (refereegranskat)abstract
- Fear conditioning is a traditional model for the acquisition of fears and phobias. Studies of the genetic architecture of fear conditioning may inform gene-finding strategies for anxiety disorders. The objective of this study was to determine the genetic and environmental sources of individual differences in fear conditioning by means of a twin sample. METHODS: Classic fear conditioning data were experimentally obtained from 173 same-sex twin pairs (90 monozygotic and 83 dizygotic). Sequences of evolutionary fear-relevant (snakes and spiders) and fear-irrelevant (circles and triangles) pictorial stimuli served as conditioned stimuli paired with a mild electric shock serving as the unconditioned stimulus. The outcome measure was the electrodermal skin conductance response. We applied structural equation modeling methods to the 3 conditioning phases of habituation, acquisition, and extinction to determine the extent to which genetic and environmental factors underlie individual variation in associative and nonassociative learning. RESULTS: All components of the fear conditioning process in humans demonstrated moderate heritability, in the range of 35% to 45%. Best-fitting multivariate models suggest that 2 sets of genes may underlie the trait of fear conditioning: one that most strongly affects nonassociative processes of habituation that also is shared with acquisition and extinction, and a second that appears related to associative fear conditioning processes. In addition, these data provide tentative evidence of differences in heritability based on the fear relevance of the stimuli. CONCLUSION: Genes represent a significant source of individual variation in the habituation, acquisition, and extinction of fears, and genetic effects specific to fear conditioning are involved.
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| 3. |
- Hettema, John M., et al.
(författare)
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The genetic covariation between fear conditioning and self-report fears
- 2008
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Ingår i: Biological Psychiatry. - : Elsevier BV. - 0006-3223 .- 1873-2402. ; 63:6, s. 587-593
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Tidskriftsartikel (refereegranskat)abstract
- Background: Fear conditioning is a traditional model for the acquisition of phobias, whereas behavioral therapies use processes underlying extinction to treat phobic and other anxiety disorders. Furthermore, fear conditioning has been proposed as an endophenotype for genetic studies of anxiety disorders. Although prior studies have demonstrated that fear conditioning and self-report fears are heritable, no studies have determined whether they share a common genetic basis. Methods: We obtained fear conditioning data from 173 twin pairs from the Swedish Twin Registry who also provided self-report ratings of 16 common fears. With multivariate structural equation modeling, we analyzed factor-derived scores for the subjective fear ratings together with the electrophysiologic skin conductance responses during habituation, acquisition, and extinction to determine the extent of their genetic covariation. Results: Phenotypic correlations between experimental and self-report fear measures were modest and, counter-intuitively, negative (i.e., subjects who reported themselves as more fearful had smaller electrophysiologic responses). Best-fit models estimated a significant (negative) genetic correlation between them, although genetic factors underlying fear conditioning accounted for only 9% of individual differences in self-report fears. Conclusions: Experimentally derived fear conditioning measures share only a small portion of the genetic factors underlying individual differences in subjective fears, cautioning against relying too heavily on the former as an endophenotype for genetic studies of phobic disorders.
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| 4. |
- Kendler, Kenneth S., et al.
(författare)
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A longitudinal twin study of fears from middle childhood to early adulthood : evidence for a developmentally dynamic genome
- 2008
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Ingår i: Archives of General Psychiatry. - : American Medical Association (AMA). - 0003-990X .- 1538-3636. ; 65:4, s. 421-429
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Tidskriftsartikel (refereegranskat)abstract
- Context: While the nature of common fears changes over development, we do not know whether genetic effects on fear-proneness are developmentally stable or developmentally dynamic. Objective: To determine the temporal pattern of genetic and environmental effects on the level of intensity of common fears. Design: Prospective, 4-wave longitudinal twin study. Structural modeling was performed with Mx. Setting: General community. Participants: Two thousand four hundred ninety twins and their parents from the Swedish Twin Study of Child and Adolescent Development. Main Outcome Measure: The level of parent- and/or self-reported fears obtained at ages 8 to 9, 13 to 14, 16 to 17, and 19 to 20 years. Results: Thirteen questionnaire items formed 3 distinct fear factors: situational, animal, and blood/injury. For all 3 fears, the best-fit model revealed developmentally dynamic effects and, in particular, evidence for both genetic attenuation and innovation. That is, genetic factors influencing fear intensity at age 8 to 9 years decline substantially in importance over time. Furthermore, new sets of genetic risk factors impacting fear intensity "come on line" in early adolescence, late adolescence, and early adulthood. As the twins aged, the influence of the shared environment declined and unique environment increased. No sex effects were found for situational fears while for animal and blood/injury fears, genetic factors in males and females were correlated but not identical. Shared environmental factors were both more important and,more stable for animal fears than for situational or blood/injury fears. Conclusions: Genetic effects on fear are developmentally dynamic from middle childhood to young adulthood. As children age, familial-environmental influences on fears decline in importance.
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