Environmental Factors Play a Role in Psychotic Experiences for Adolescent Twins

Mark J. Taylor, PhD

Environmental factors such as bullying and substance use could play a factor 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 risks linked to psychotic experiences in adolescence patients using the twin design.

Unknown Factors

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

However, there is not much known whether the risk factors of psychotic experiences interact with environmental risks for psychotic experiences.

Studying Twins

In the twin study, the investigators examined 4855 twin pairs from a UK-based sample of twin pairs aged 16 years between December 1, 2014 and August 31, 2020 and evaluated the extent of genetic variance underlying psychotic experiences and the magnitude of the heritability of psychotic experience 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, dependent life events, cannabis use, tobacco use, and low birth weight.

The team assessed psychotic experienced using 5 self-reported measures and 1 parent-reported measure and assessed patient exposure to environmental risks ages 12-16 years.

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

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

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

Environmental Risk Factor Exposure

The results show more exposure to environmental risk factors is linked 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%).

The investigators found the pattern replicated in the Swedish cohort.

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

“Findings 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 among individuals exposed to environmental risks for psychotic experiences, highlighting 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.