Neurocognitive-genetic and neuroimaging-genetic research paradigms in schizophrenia and bipolar disorder

Studies examining intermediate phenotypes such as neurocognitive and neuroanatomical measures along with susceptibility genes are important for improving our understanding of the neural basis of schizophrenia (SZ) and bipolar disorder (BD). In this paper, we review extant studies involving neurocognitive-genetic and neuroimaging-genetic perspectives and particularly related to catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF) and neuregulin-1 (NRG1) genes in SZ and BD. In terms of neurocognitive-genetic investigations, COMT and BDNF are the two most studied candidate genes especially in patients with SZ. Whereas BDNF Met carriers perform worse on verbal working memory, problem solving and visuo-spatial abilities, COMT Met carriers perform better in working memory, attention, executive functioning with evidence of genotype by diagnosis interactions including high-risk individuals. In terms of genetic-structural MRI studies, patients with SZ are found to have reductions in the frontal, temporal, parietal cortices, and limbic regions, which are associated with BDNF, COMT, and NRGI genes. Genetic-functional MRI studies in psychotic disorders are sparse, especially with regard to BD. These neurocognitive and neuroimaging findings are associated with genes which are implicated in functional pathways related to neuronal signaling, inter-neuronal communication and neuroplasticity.