It was well recognized that genetic risk factors contributed to the genesis of psychotic episodes in the general population. It was unclear how these risk factors and environmental dangers for psychotic episodes interacted. For a study, researchers sought to employ a twin design, determine the environmental risk exposure and etiological heterogeneity of adolescent psychotic events.

A sample of twin pairs aged 16 years old from the UK were involved in the twin research, which was undertaken from December 1, 2014, to August 31, 2020. The study looked at how exposure to five environmental risk variables affected the genetic variation that underlies psychotic experiences and how much psychotic experiences are heritable (bullying, dependent life events, cannabis use, tobacco use, and low birth weight). Five self-report measures and one parent-report measure were used to evaluate psychotic events. During birth and at ages 12 to 16, participants’ exposure to environmental dangers was evaluated. While accounting for the effects of gene-environment association, structural equation models were used to compare the variance and heritability of psychotic episodes across various exposures. In a different Swedish sample, analyses were conducted once again. Analyses of the data were done between September 1, 2018, and August 31, 2020.

The Twins Early Development Study (TEDS) included a total of 4,855 twin pairs (1,926 female same-sex pairs, 1,397 male same-sex pairs, and 1,532 opposite-sex pairs), and the Child and Adolescent Twin Study in Sweden (CATSS) included 6,435 twin pairs (2,358 female same-sex pairs, 1,861 male same-sex pairs, and 2,216 opposite-sex pairs). The twins from the TEDS had a mean age of 16.5 years. Twins from the CATSS had an average age of 18.6 years. There was a correlation between having more psychotic episodes and being exposed to more environmental risk factors. The relative contribution of genetic factors to psychotic experiences decreased 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%). In the independent Swedish replication sample, the same trend was repeated for the measure of psychotic events. The heritability of hallucinations and negatively reported symptoms by parents stayed largely the same.

The results of the twin study indicated that environmental variables rather than genetic ones were more important in the genesis of psychotic symptoms. The usefulness of a diathesis-stress or bioecological paradigm for explaining teenage psychotic episodes was shown by the fact that the relative impact of environmental variables was even higher among those who are exposed to environmental hazards for psychotic experiences.