Objective: Psychotic disorders were previously associated with catechol- O-methyltransferase (COMT) val158met (rs4680) and brain-derived neurotrophic factor (BDNF) val66met (rs6265) polymorphisms. This article evaluates the association between COMT/BDNF polymorphisms and the extended psychosis phenotype which covers not only schizophrenia but also subclinical expressions of psychotic experiences.
Method: The participants of this study were part of the TürkSch (Izmir Mental Health Survey for Gene-Environment Interaction in Psychoses), a longitudinal study Psychotic experiences and disorders were screened 437. The extended psychosis phenotype was grouped into four: (1) no psychotic experiences (n: 194), (2) subclinical psychotic experiences (n: 87), (3) clinically relevant psychotic experiences (n: 104), and (4) schizophrenia-like disorders (n: 52). BDNF rs6265 was genotyped occurred in every participant whereas COMT rs4680 genotyping could be done on 366 individuals.
Results: There was no association between the extended psychosis phenotype and BDNF rs6265/COMT rs4680 polymorphisms. The frequency of met carriers in the BDNF rs6265genotype was slightly higher in individuals with subclinical psychotic experiences than in the group with no psychotic experiences, which was just below the significance level (p=0.08).
Conclusion: The lack of an association between different expression levels of the extended psychosis phenotype and the BDNF rs6265/ COMT rs4680 polymorphism might be related to sample characteristics, underlying gene-gene, gene-environment and gene-environment-gene interactions.