title: A longitudinal twin study of fears from middle childhood to early adulthood: evidence for a developmentally dynamic genome.
abstract: BACKGROUND
  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.
  
  
  METHODS
  Prospective, 4-wave longitudinal twin study. Structural modeling was performed with Mx.
  
  
  METHODS
  General community.
  
  
  METHODS
  Two thousand four hundred ninety twins and their parents from the Swedish Twin Study of Child and Adolescent Development.
  
  
  METHODS
  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.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University Medical School, Box 980126, 800 E Leigh St, Room 1-123, Richmond, VA 23298-0126, USA. kendler@vcu.edu
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.forename: Charles O
authors.initials: CO
authors.lastname: Gardner
authors.forename: Peter
authors.initials: P
authors.lastname: Annas
authors.forename: Michael C
authors.initials: MC
authors.lastname: Neale
authors.forename: Lindon J
authors.initials: LJ
authors.lastname: Eaves
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005239:Fear; D005260:Female; D005500:Follow-Up Studies; D016678:Genome; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015588:Observer Variation; D010698:Phobic Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D014427:Twins / Q000235:genetics*