Language lateralization in monozygotic twins discordant and concordant for schizophrenia. A functional MRI pilot study

Aim: Previous studies have suggested altered structural and functional asymmetry of the brain in schizophrenia. Methods: Functional MRI was used to assess differences in cortical activation during a verbal task in Broca's area and its contralateral homologue in four pairs of right-handed monozygotic (MZ) twins discordant and concordant for schizophrenia with low and high familial loading for the illness and four healthy control MZ twin pairs. Results: Pooled data from all subjects with schizophrenia showed increased activation in the right homologue of Broca's area in contrast to healthy individuals. Concordant twins (i.e. high familial loading group) showed prominent between co-twin differences in lateralization index within given region of interest. Intra-pair differences in lateralization index were significantly higher in concordant twins compared to the controls (0.69 ± 0.4 vs. 0.13 ± 0.13, P < 0.03), albeit no significant differences in the variable were shown between the discordant and control groups. Conclusion: This study provides evidence of reduced cerebral dominance for language processing in patients with schizophrenia. The findings further suggest the need for additional research on relative proportion of genetic and environmental factors underlying deviations of functional asymmetry in schizophrenia.