Environmental factors play a role in the psychotic experiences of adolescent twins

Environmental factors such as bullying and substance use might play a role in the etiological heterogeneity of psychotic experiences.

A team, led by Mark J. Taylor, PhD, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, assessed etiological heterogeneity and exposure to environmental hazards related to psychotic experiences in adolescent patients using the design of twins.

Unknown factors

Genetic factors may play a role in the etiology of psychotic experiences in most individuals.

However, it is unclear whether risk factors for psychotic experiences interact with environmental risks for psychotic experiences.

Study twins

In the twin study, investigators examined 4,855 sets of twins from a UK-based sample of 16-year-old twin sets between December 1, 2014 and August 31, 2020 and assessed the extent of genetic variance underlying psychotic experiences and the extent of heritability of psychotic experiences moderated by environmental factors.

The patient population included 1926 female same-sex pairs, 1397 male same-sex pairs, and 1532 opposite-sex pairs from the Twins Early Development Study (TEDS).

The analysis included 5 environmental factors – bullying, addicted life events, cannabis use, tobacco use and low birth weight.

The team assessed psychotic experience using 5 self-reported measures and 1 parent-reported measure and assessed patients’ exposure to environmental hazards aged 12-16 years.

They used structural equation models to assess differences in variance and heritability of psychotic experiences across exposures, while controlling for gene-environment correlation effects and also repeated analyzes in an independent Swedish sample. which included 6435 pairs of twins, including 2358 women. same-sex couples, 1861 male same-sex couples and 2216 opposite-sex couples from the Child and Adolescent Twins Study in Sweden (CATSS).

The investigators looked for primary outcome measures of exposure to environmental factors measured by a composite score and psychotic experiences.

The average age of twins in the UK sample was 16.5 years and the average age of twins in the Swedish sample was 18.6 years.

Exposure to environmental risk factors

The results show that greater exposure to environmental risk factors is related to having more psychotic experiences, while the relative contribution of genetic influences to psychotic experiences was lower with increasing environmental exposure. for paranoia (44%; 95% CI, 33-53% to 38%; 95% CI, 14-58%), cognitive disorganization (47%; 95% CI, 38-51% to 32%; 95% CI, 11-45%), grandiosity (41%; 95% CI, 29-52% to 32%; 95% CI, 9-48%) and anhedonia (49%; 95% CI, 42-53% to 37%; 95% CI, 15-54%).

Investigators found the pattern replicated in the Swedish cohort.

They also found that the heritability of parent-related hallucinations and negative symptoms was relatively consistent.

“The results of this twin study suggest that environmental factors play a greater role in the etiology of psychotic experiences than genetic factors,” the authors wrote. “The relative importance of environmental factors is even higher in individuals at environmental risk for psychotic experiences, underscoring the importance of a diathesis-stress or bioecological framework for understanding adolescent psychotic experiences.”

The study, “Heritability of Psychotic Experiences in Adolescents and Interaction with Environmental Risk,” was published online in JAMA Psychiatry.