The genetic factors that are associated with fears seem to change as children and adolescents age. According to a report in the April issue of the Archives of General Psychiatry, a JAMA/Archives journal, some hereditary factors decrease in importance while others appear or become more important over time.
During childhood and adolescent development, the nature itself of common fears change. There are two major hypotheses proposed for the genetic basis of this observation. According to the authors: “The ‘developmentally stable’ hypothesis predicts that a single set of genetic risk factors impacts the level of fears at age 8 years and these same genes constitute the only genetic influences on fear-proneness throughout development.” They continue,”By contrast, the ‘developmentally dynamic’ hypothesis predicts that genetic effects on fear-proneness will vary over time.”
To investigate these hypotheses, Kenneth S. Kendler, M.D., of the Virginia Commonwealth University School of Medicine, Richmond, and colleagues examined twins born in Sweden between 1985 and 1986. At four different time points, the twins were assessed for their levels of fear: at age 8-9 by a questionnaire mailed to the parents; at ages 13-14 and 16-17 with questionnaires mailed to twins and parents; and at age 19-20 with questionnaires mailed only to the twins.
The fears reported divided largely into three categories. The first was of situational fears, such as the fear of closed spaces, of flying, or of the dark. The second involved animals, for example rats, dogs, or snakes. Finally, some fears involved blood or injury — these included the fear of dentists, of injections, or of blood. Generally, genetic factors were linked to all three types of fears, but these factors were not stable over time.
As the twins got older, the effects of their shared environment diminished while the influence of their individual environments increased. According to the authors, this is fairly logical: “This is an expected pattern given that adolescence is a time of declining influence of the home environment as individuals spend less time with family and progressively make their own world, spending more time with friends”
The authors also state that they have found new genetic risk factors that influence these fears: “We identified one set of genetic risk factors that act in childhood and have a steep decline in influence with age.” They continue to indicate that more could be found: “Furthermore, we see evidence for new sets of genetic risk factors ‘coming on line’ in early adolescence, late adolescence and early adulthood.” Future research should point towards determining the exact mechanisms by which these genetic factors influence fears, they say. For instance, if genes that influence mental process, such as sensitivity or disgust, are closely linked to changes in neurobiology, including alterations in the brain circuits that process fears, it could have profound effects on the field.
A Longitudinal Twin Study of Fears From Middle Childhood to Early Adulthood: Evidence for a Developmentally Dynamic Genome
Kenneth S. Kendler, MD; Charles O. Gardner, PhD; Peter Annas, PhD; Michael C. Neale, PhD; Lindon J. Eaves, PhD, DSc; Paul Lichtenstein, PhD
Arch Gen Psychiatry. 2008;65(4):421-429.
Written by Anna Sophia McKenney