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Environmental risk factors may play a larger role than genetic factors in the development of psychotic experiences in adolescents, according to a twin study in Europe.

Among over 11,000 twin pairs, the relative contribution of genetic influences to cognitive disorganization was 47% in those with no exposure to environmental risk factors -- such as bullying, dependent life events, cannabis use, tobacco use, or low birth weight -- compared with 32% in those with these exposures, reported Angelica Ronald, PhD, of Birkbeck University of London in England, and co-authors in

Furthermore, paranoia heritability changed from 44% to 38% with increasing exposure, grandiosity heritability changed from 41% to 32%, and anhedonia heritability changed from 49% to 37%, they noted, while heritability for hallucinations was found to be relatively constant regardless of exposure to environmental risk factors.

"Clinicians may have learned at some point in their training that some psychiatric conditions are extremely highly heritable -- that they run in families -- and there's evidence for that," Ronald told 麻豆传媒. "But it looks like there may also be a pathway toward mental health difficulties in teenagers that is more driven by environmental exposures."

She noted that the study was designed to test observations shared with her by clinicians who noticed the influence of environmental factors in their patients.

"We have previously known that environmental adversity is likely to be important for mental health problems," Ronald said. "Equally, we've got a lot of evidence that genes play a role. But it wasn't really clear how they were operating together. Our results show evidence for what we call gene-environment interaction."

Laramie Duncan, PhD, of Stanford University in California, said this evidence is compelling because these environmental risk factors can be changed.

"It's important to know how much environmental factors matter for psychotic experiences, and especially to know that environmental factors are rather important for psychotic experiences in adolescents," Duncan told 麻豆传媒 in an email. "The good news is that environmental factors are more easily modified than genetic factors."

Ronald highlighted the correlation between psychotic experiences and psychiatric outcomes later in life, noting that these findings are "an important early kind of red flag for potential need for support."

Duncan agreed that these findings have clinical implications, adding that "currently available interventions will help to reduce these symptoms. That's good news for parents, clinicians, and communities."

For this study, conducted from December 2014 through August 2020, Ronald and team included 4,855 twin pairs (1,926 female pairs, 1,397 male pairs, and 1,532 opposite-sex pairs) from the Twins Early Development Study in the U.K. and 6,435 twin pairs (2,358 female pairs, 1,861 male pairs, and 2,216 opposite-sex pairs) from the Child and Adolescent Twin Study in Sweden. Mean age was 16.5 years in the U.K. cohort and 18.6 years in the Swedish cohort.

Participants were evaluated for exposure to the five environmental risk factors at birth and from ages 12 to 16. They were also assessed for psychotic experiences using five self-reported measures and one parent-reported measure.

Ronald and colleagues acknowledged that their study only focused on data from two European countries, and their findings may not be applicable to other populations.

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