Environment plays larger role than genetics for psychotic experiences in adolescents

Environmental factors play a greater role in the genesis of psychotic experiences than genetic factors among adolescents, according to a study published in JAMA Psychiatry.

“Psychotic experiences, such as paranoia and hallucinations, are relatively common in adolescence, with an estimated prevalence of 5% in adults,” Mark J. Taylor, PhD, of the department of medical epidemiology and biostatistics at Karolinska Institute in Stockholm, and colleagues wrote. “Factors found to be associated with psychotic experiences include bullying and childhood maltreatment, life events, cannabis use and tobacco use.”

Taylor and fellow researchers aimed to assess etiological heterogeneity and exposure to environmental risks associated with psychotic experiences in adolescence by analyzing sets of twins.

The study, conducted from December 2014, through August 2020, included a United Kingdom-based sample of 4,855 twin pairs (1,926 female same-sex pairs, 1,397 male same-sex pairs, 1,532 opposite-sex pairs; mean age, 16.5 years) from the Twins Early Development Study, along with 6,435 twin pairs (2,358 female same-sex pairs, 1,861 male same-sex pairs, 2,216 opposite-sex pairs; mean age, 18.6 years) from the Child and Adolescent Twin Study in Sweden.

Researchers evaluated the extent to which the genetic variance underlying psychotic experiences and the magnitude of the heritability of psychotic experiences was moderated by exposure to five environmental risk factors — bullying, dependent life events, cannabis use, tobacco use and low birth weight.

Psychotic experiences were assessed by five self-reported measures and one parent-reported measure. Participants’ exposure to environmental risks was assessed at birth, then between those aged 12 to 16 years. Structural equation models were used to assess differences in the variance in and heritability of psychotic experiences across these exposures, while controlling for gene-environment correlation effects. Primary outcome measures were exposure to environmental factors, as measured by a composite score, and psychotic experiences.

Results showed that more exposure to environmental risk factors was associated with having more psychotic experiences. 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 lack of ability to take pleasure in activities (49%; 95% CI, 42%-53% to 37%; 95% CI, 15%-54%).

The pattern was replicated in the independent Swedish replication sample. The heritability of hallucinations and parent-rated negative symptoms remained relatively constant.

“It is an important message that early manifestations of psychotic experiences during adolescence are not so strongly heritable, especially in the context of higher environmental exposure,” Taylor and colleagues wrote.