a1 Virginia Institute of Psychiatric and Behavioral Genetics, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA, USA
a2 Department of Psychiatry, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA, USA
a3 Department of Human Genetics, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA, USA
a4 Department of Psychology, Uppsala University, Uppsala, Sweden
a5 Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden
Background Common fears change over development. Genetic and environmental risk factors for fears are partly shared across fears and partly fear-specific. The nature of the changes in common and fear-specific genetic and environmental risk factors over time is unknown.
Method Self-reported fears were obtained at ages 13–14, 16–17 and 19–20 from 2404 twins in the Swedish Twin Study of Child and Adolescent Development. A multivariate longitudinal twin analysis was conducted with Mx.
Results Eighteen individual items formed four fear factors: animal, blood-injury, situational, and social. The best-fit model had no quantitative or qualitative sex effects or shared environmental effects, but included a strong common factor with a stable cross-time structure with highest loadings on situational and lowest loadings on social fears. New common and fear-specific genetic risk factors emerged over development. With increasing age, genetic effects declined in overall importance and became more fear-specific. Cross-time continuity in specific genetic effects was highest for animal and lowest for social fears. Social fears had a ‘burst’ of specific genetic effects in late adolescence. Individual-specific environmental factors impacted both on the general fear factor and on specific fears. Compared to genetic effects, the impact of the unique environment was more time-specific.
Conclusions Genetic and environmental risk factors for individual fears are partly mediated through a common fear factor and are partly fear-specific in their effect. The developmental pattern of these risk factors is complex and dynamic with new common and specific genetic effects arising in late adolescence and early adulthood.
(Received July 30 2007)
(Revised December 20 2007)
(Accepted December 24 2007)
(Online publication February 25 2008)
c1 Address for correspondence: K. S. Kendler, M.D., Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University Medical School, Box 980126, 800 E. Leigh Street, Room 1-123, Richmond, VA 23298-0126, USA. (Email: email@example.com)