Washington, Apr 8 : A new study has shown that common fears in humans are linked to genetic factors, which keep changing as children and adolescents age.
The study found that genetic factors linked with fears appear to change as children and adolescents age, with some familial factors losing their importance over time while other genetic risk factors arising in adolescence and adulthood.
The study by Kenneth S. Kendler, M.D., of the Virginia Commonwealth University School of Medicine, Richmond, has recommended two hypotheses regarding genetic risk factors for these fears.
"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. By contrast, the 'developmentally dynamic' hypothesis predicts that genetic effects on fear-proneness will vary over time," wrote the authors.
For the study, the researchers examined 2,490 twins born in Sweden between 1985 and 1986, who were later assessed for their level of fear four times: at age 8 to 9 by a questionnaire mailed to parents, at ages 13 to 14 and 16 to 17 with questionnaires mailed to twins and parents and at age 19 to 20 with questionnaires only to the twins.
The researchers naturally divided fears into three categories: situational fears (such as fear of closed spaces, flying or the dark), animal fears (including rats, dogs and snakes) and blood or injury fears (fears of dentists, injections and blood). On the whole, genetic factors influenced all three types of fears, but did not remain stable over time.
"We identified one set of genetic risk factors that act in childhood and have a steep decline in influence with age. Furthermore, we see evidence for new sets of genetic risk factors 'coming on line' in early adolescence, late adolescence and early adulthood," the authors stated.
It was found that with increase in age, effects of the twins' shared environment on their fears diminished and the influence of their individual environment increased.
"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 wrote.
The study is published in the latest issue of Archives of General Psychiatry, one of the JAMA/Archives journals.