Environmental factors outweigh the role of genetic factors in the cause of psychotic experiences among adolescents, and environment is even more significant among individuals subjected to environmental risks for psychotic experiences. These are some of the study findings published in the Journal of the American Medical Association Psychiatry.
Genetic risk factors contribute to the etiology of psychotic experiences. It is believed that environmental factors of bullying and childhood abuse, cannabis and tobacco use, obstetric complications, and life events also contribute to this etiology. It is unclear how/if these risk factors interact with the environmental risks for psychotic experiences. Researchers aimed to assess exposure to environmental risks and etiological heterogeneity associated with psychotic experiences in adolescence.
They conducted twin cohort studies between November 2014 and September 2020 that included the Twins Early Development Study (TEDS; twins mean age, 16.5 years) born in the United Kingdom, and the Child and Adolescent Twin Study in Sweden (CATSS; twins mean age, 18.6 years) born in Sweden. Exposure variables included bullying, dependent life events, cannabis use, tobacco use, and low birth weight.
Researchers used SPEQ which breaks down into 5 self-reported subscales (paranoia, hallucinations, cognitive disorganization, grandiosity, and anhedonia) and 1 parent-reported measure to assess psychotic experiences. Analysis of TEDS was repeated in CATSS. The primary outcomes were environmental factor exposure measured by psychotic experiences and a composite score.
There were 4855 twin pairs (1926 girl same-sex pairs, 1397 boy same-sex pairs, and 1532 opposite-sex pairs) included from TEDS, and 6435 twin pairs (2358 girl same-sex pairs, 1861 boy same-sex pairs, and 2216 opposite-sex pairs) included from CATSS. Greater exposure to environmental risk factors associated with more psychotic experiences.
Researchers found in the TEDS cohort that the relative role of genetic influences to psychotic experiences decreased as environmental exposure increased for cognitive disorganization (47%; 95% CI, 38%-51% vs 32%; 95% CI, 11%-45%, respectively), grandiosity (41%; 95% CI, 29%-52% vs 32%; 95% CI, 9%-48%, respectively), paranoia (44%; 95% CI, 33%-53% vs 38%; 95% CI, 14%-58%, respectively), and anhedonia (49%; 95% CI, 42%-53% vs 37%; 95% CI, 15%-54%, respectively) compared with patients in the CATSS cohort. They noted that this pattern for the measure of psychotic experiences was replicated in the CATSS cohort, and that the parent-rated negative symptoms and heritability of hallucinations stayed fairly constant.
Study limitations include nongeneralizability to populations where exposures differ in prevalence, measure of tobacco and cannabis use may have been too brief, the use of a composite score which included summing exposures with varying underlying etiologies, the use of birth weight, environmental composite not identical across TEDS and CATSS, exclusion criteria varied between TEDS and CATSS, and the possibility of response bias in teenage self-reported measures.
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 among individuals exposed to environmental risks for psychotic experiences, highlighting the importance of a diathesis-stress or bioecological framework for understanding adolescent psychotic experiences.”
Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Taylor MJ, Freeman D, Lundström S, Larsson H, Ronald A. Heritability of psychotic experiences in adolescents and interaction with environmental risk. JAMA Psychiatry. Published online August 3, 2022. doi:10.1001/jamapsychiatry.2022.1947