Four genetic variations appear to link psychotic experiences with other psychiatric disorders, including schizophrenia, major depressive disorder, bipolar disorder, and neurodevelopmental disorders, a large genetic study has concluded.
, reported Sophie E. Legge, PhD, and colleagues. Their study was published in JAMA Psychiatry.
Although it is informative, the study is unlikely to expand the knowledge of schizophrenia-specific genetics.
“Consistent with other studies, the heritability estimate (1.71%) was low, and given that the variance explained in our polygenic risk analysis was also low, the finding suggests that understanding the genetics of psychotic experiences is unlikely to have an important effect on understanding the genetics of schizophrenia specifically,” wrote Dr. Legge, of the MRC Center for Neuropsychiatric Genetics and Genomics in the division of psychological medicine and clinical neurosciences at Cardiff (Wales) University, and colleagues.
The team conducted a genomewide association study (GWAS) using data from 127,966 individuals in the U.K. Biobank. Of these, 6,123 reported any psychotic experience, 2,143 reported distressing psychotic experiences, and 3,337 reported multiple experiences. The remainder served as controls. At the time of the biobank data collection, the subjects were a mean of 64 years of age; 56% were women.
First psychotic experience occurred at a mean of almost 32 years of age, but about a third reported that the first episode occurred before age 20, or that psychotic experiences had been happening ever since they could remember. Another third reported their first experience between ages 40 and 76 years.
The investigators conducted three GWAS studies: one for any psychotic experience, one for distressing experiences, and one for multiple experiences.
No significant genetic associations were found among those with multiple psychotic experiences, the authors said.
But they did find four variants significantly associated with the other experience categories.
Two variants were associated with any psychotic experience. Those with rs10994278, an intronic variant within Ankyrin-3 (ANK3), were 16% more likely to have a psychotic experience (odds ratio, 1.16). Those with intergenic variant rs549656827 were 39% less likely (OR, 0.61). “The ANK3 gene encodes ankyrin-G, a protein that has been shown to regulate the assembly of voltage-gated sodium channels and is essential for normal synaptic function,” the authors said. “ANK3 is one of strongest and most replicated genes for bipolar disorder, and variants within ANK3 have also been associated in the Psychiatric Genomics Consortium cross-disorder GWAS, and in a rare variant analysis of autism spectrum disorder.”
Two variants were linked to distressing psychotic experiences: rs75459873, intronic to cannabinoid receptor 2 (CNR2), decreased the risk by 34% (OR, 0.66). Intergenic variant rs3849810 increased the risk by 12% (OR, 1.12).
“CNR2 encodes for CB2, one of two well-characterized cannabinoid receptors. Several lines of evidence have implicated the endocannabinoid system in psychiatric disorders, including schizophrenia and depression. The main psychoactive agent of cannabis, tetrahydrocannabinol, can cause acute psychotic symptoms and cognitive impairment. Given that cannabis use is strongly associated with psychotic experiences, we tested, but found no evidence for, a mediating or moderating effect of cannabis use on the association of rs75459873 and distressing psychotic experiences. However, while no evidence was found in this study, a mediating effect of cannabis use cannot be ruled out given the relatively low power of such analyses and the potential measurement error.”
Also, significant genetic correlations were found between any psychotic experiences and major depressive disorder, autism spectrum disorder, ADHD, and schizophrenia. However, the polygenic risk scores for schizophrenia, major depressive disorder, bipolar disorder, ADHD, and autism spectrum disorder, were low.
“We also considered individual psychotic symptoms and found that polygenic risk scores for schizophrenia, bipolar disorder, depression, and ADHD were more strongly associated with delusions of persecution than with the other psychotic symptoms.”
Those with distressing psychotic experiences tended to have more copy number variations (CNVs) associated with schizophrenia (OR, 2.04) and neurodevelopmental disorders (OR, 1.75). The team also found significant associations between distressing experiences and major depressive disorder, ADHD, autism spectrum disorder, and schizophrenia.
“We found particular enrichment of these [polygenic risk scores] in distressing psychotic experiences and for delusions of persecution,” they noted. “ ... All schizophrenia-associated [copy number variations] are also associated with neurodevelopmental disorders such as intellectual disability and autism.”
The study’s strengths include its large sample size. Among its limitations, the researchers said, are the study’s retrospective measurement of psychotic experiences based on self-report from a questionnaire that was online. Gathering the data in that way raised the likelihood of possible error, they said.
Dr. Legge reported having no disclosures.
SOURCE: Legge SE et al. JAMA Psychiatry. 2019 Sep 25. doi: 10.1001/jamapsychiatry.2019.2508.