Environmental factors outweigh the role of genetic factors in causing psychotic experiences in adolescents, and the environment is even more important in individuals at environmental risk for psychotic experiences. Here are some of the study results published in the American Medical Association Journal of Psychiatry.
Genetic risk factors contribute to the etiology of psychotic experiences. Environmental factors of bullying and childhood abuse, cannabis and tobacco use, obstetric complications, and life events are also thought to contribute to this etiology. It is unclear how/if these risk factors interact with environmental risks of psychotic experiences. The researchers aimed to assess environmental risk exposure and etiological heterogeneity associated with psychotic experiences in adolescence.
They conducted twin cohort studies between November 2014 and September 2020 which included the Twins Early Development Study (TEDS; mean age of twins, 16.5 years) born in the UK, and the Child and Adolescent Twin Study in Sweden (CATSS; average age of twins 18.6) born in Sweden. Exposure variables included bullying, addicted life events, cannabis use, tobacco use, and low birth weight.
The researchers used the SPEQ which is broken down into 5 self-reported subscales (paranoia, hallucinations, cognitive disorganization, grandiosity, and anhedonia) and 1 parent-reported measure to assess psychotic experiences. The TEDS analysis was repeated in CATSS. The primary outcomes were exposure to environmental factors measured by psychotic experiences and a composite score.
There were 4,855 twin pairs (1,926 same-sex girl pairs, 1,397 same-sex boy pairs, and 1,532 opposite-sex pairs) included in the TEDS, and 6,435 twin pairs (2,358 same-sex girl pairs, 1,861 same-sex pairs of boys, and 2,216 opposite-sex pairs) included in the CATSS. Greater exposure to environmental risk factors associated with more psychotic experiences.
The researchers found in the TEDS cohort that the relative role of genetic influences on psychotic experiences decreased as environmental exposure increased for cognitive disorganization (47%; 95% CI, 38% to 51% vs. 32%; 95% CI, 11% to 45%, respectively), grandiosity (41%; 95% CI, 29%-52% versus 32%; 95% CI, 9%-48%, respectively), paranoia (44 %; 95% CI, 33%-53% versus 38%; 95% CI, 14%-58%, respectively) and anhedonia (49%; 95% CI, 42%-53% versus 37% 95% CI, 15% to 54%, respectively) compared to patients in the CATSS cohort. They noted that this pattern of measuring psychotic experiences was replicated in the CATSS cohort and that parent-rated negative symptoms and heritability of hallucinations remained fairly constant.
Limitations of the study include not generalizing to populations where exposures differ in terms of prevalence, measurement of tobacco and cannabis use may have been too brief, use of a composite score that included the sum exposures with different underlying etiologies, use of birth weight, environmental composite not identical across study. TEDS and CATSS, exclusion criteria varied between TEDS and CATSS, and the possibility of response bias in adolescent self-report measures.
The researchers concluded that their findings suggest that “environmental factors play a greater role in the etiology of psychotic experiences than genetic factors.” They added that “the relative importance of environmental factors is even higher in individuals exposed to environmental risks of psychotic experiences, highlighting the importance of a diathesis-stress or bioecological framework for understanding adolescent psychotic experiences” .
Disclosure: Some study authors have disclosed affiliations with biotechnology, pharmaceutical and/or device companies. Please see the original citation for a full list of author disclosures.
Taylor MJ, Freeman D, Lundström S, Larsson H, Ronald A. Heritability of adolescent psychotic experiences and interaction with environmental risk. JAMA Psychiatry. Published online August 3, 2022. doi:10.1001/jamapsychiatry.2022.1947