Environmental factors play major role in etiology of psychotic experiences than genetic factor: JAMA

Sweden: A new study found that environmental factors play a major role in the etiology of psychotic experiences than genetic factors. The article was published in the JAMA Psychiatry.

Paranoia and hallucinations are relatively common psychotic experiences seen in adolescence. Considerable progress has been made in understanding the etiology of psychotic experiences, including moderate twin heritability and single-nucleotide variation heritability. Genetic risk factors are known to play a role in the etiology of psychotic experiences in the general population, but very little is known about whether these risk factors interact with environmental risks for psychotic experiences.

Previous studies have shown that genetic and environmental influences on psychotic experiences do not operate independently of one another. This may also occur through gene-by-environment interaction, whereby the importance of genetic influences may vary depending on environmental exposure and vice versa.

Taylor MJ, Karolinska Institutet, Stockholm, Sweden, and colleagues conducted a study to assess etiological heterogeneity and exposure to environmental risks associated with psychotic experiences in adolescence using the twin design.

For the study, a total of 4855 twin pairs were included from the Twins Early Development Study (TEDS), and 6435 twin pairs from the Child and Adolescent Twin Study in Sweden (CATSS). The mean age of twins was 16years. 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 5 environmental risk factors (bullying, dependent life events, cannabis use, tobacco use, and low birth weight).

Psychotic experiences were assessed by 5 self-reported measures and 1 parent-reported measure. Participants' exposure to environmental risks was assessed at birth and at age 12 to 16 years. Primary outcome measures were exposure to environmental factors, as measured by a composite score, and psychotic experiences.

Key findings of the study:

• 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, cognitive disorganization, grandiosity, and anhedonia

• The heritability of hallucinations and parent-rated negative symptoms remained relatively constant when the pattern was replicated for the measure of psychotic experiences in the independent Swedish replication sample.

The authors conclude that the twin study was the first with results suggesting a greater role of environmental factors in the etiology of psychotic experiences than genetic factors. Most clinicians are aware that psychotic disorders are hereditary, but the results show that early manifestations of psychotic experiences during adolescence are not so strongly heritable, especially in the context of higher environmental exposure. Psychotic experiences are likely to manifest in adolescents both with and without a family history. 

Genetic and environmental risks for psychotic experiences operate in sync with each other, the authors commented.

Reference:

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 03, 2022. doi:10.1001/jamapsychiatry.2022.1947