The role of genetics in psychiatric disorders is well established, and yet, the complexity of the genetic basis for most of these disorders creates major challenges in this research area. Therefore, investigating biological markers has been an important approach in psychiatric genetic research for several decades. This dissertation presents three genetic studies dealing with possible biomarkers in different domains of human psychophysiology. The first study explored the impairment of early

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... l processing and its link to cholinergic system. Single nucleotide Polymorphism (SNP) rs904952 of cholinergic receptor nicotinic alpha 7 subunit (CHRNA7) on the performance on Backward Masking Task was found to be of significant influence (p=0.021). A second study investigates the role of dystrobrevin binding protein 1 (DTNBP1) in the regulation of cognitive processes, finding a significant influence of DTNBP1 (rs909706) on attention (p=0.030). In the third study, the effect of inetr-alpha-trypsin inhibitor heavy chain 3 (ITIH3) (rs2535629) on treatment response in schizophrenic patients was considered. Results suggest that the improvement of negative symptoms under clozapine treatment might be regulated by ITIH3 (rs2535629). These results once again underline the importance of the cholinergic system in the pathogenesis of schizophrenia, as well as the important role of DTNBP1 in regulation of cognitive processes. Furthermore, it adds evidence to the growing body of knowledge that individualized treatment for psychotic disorders might be the logical next step. Taken together, the results of these studies outline the real complexity of psychiatric disorders and stimulate the need for further research.