Elektrophysiological alterations in schizophrenia and relation of them with COMT Val158Met polymorphism

Aim: This thesis aims to investigate the alterations in electrophysiological responses of the brain in schizophrenia and the relation of these alterations with Val158Met polymorphism in COMT gene.Hypothesis: It is hypothesized that auditory evoked potential of schizophrenia patients does not differ from healthy subjects while auditory event related potentials and mismatch negativity has lower amplitudes in schizophrenia patients. Patients with Val/Val genotype in COMT gene are expected to have lower signal-to-noise ratio than patients with Met/Met genotype.Methods: 17 schiozphrenia patients and 17 healthy subjects underwent EEG recording during presentation of auditory stimuli. Latency and amplitudes of auditory evoked and event related potentials and mismatch negativity responses at 6 electrode sites (F3, F4, FCz, P3, P4, CPz) was measured. COMT Val158Met genotyping of 14 patients was performed via venous blood. These patients were grouped in terms of their genotypes and signal-to-noise ratios of event related potentials of these groups are investigated.Results: Latency of P60 component of evoked potentials is shorter in patients (FCz, P4). While P300 component of auditory event related potentials does not show significant difference between groups, patients have smaller late negativity (FCz, P3, CPz) and larger N100 amplitudes (p<.05). Schizophrenia patients have smaller mismatch negativity responses against different types and levels of sound deviations (p<.05). Patients with Val/Val genotype have larger signal-to-noise ratios in event related potentials than patients with Met/Met genotype.Conclusion: While there is a small difference between auditory evoked potentials of schizophrenia patients and healthy subjects, significant difference is observed in more components and at more electrode sites of auditory event related potentials and mismatch negativity. Smaller signal-to-noise ratio is observed in the patients with Met allele which produces less active COMT enzyme.Keywords: Schizophrenia, AEP, AERP, MMN, COMT, signal-to-noise ratio.