Background: Theory of mind (ToM) impairment has been consistently demonstrated in patients with schizophrenia, but whether ToM impairments exist in unaffected siblings of patients with schizophrenia remains unclear. Few studies have examined the affective and cognitive components of ToM in schizophrenia. This study aimed to examine whether ToM impairments exist in patients with first-episode schizophrenia and their unaffected siblings, and whether there is any dissociation between the affective and cognitive components of ToM.
Method: We adopted a family-based case-control design. Participants were 41 patients with first-episode schizophrenia, 43 unaffected siblings, and 42 healthy controls. The Yoni Task which measures the participants' ability to understand first- and second-order affective versus cognitive ToM and the Faux Pas Task which taps into integration of the affective and cognitive components of ToM were administered. Multivariate and univariate ANCOVAs were used to examine the group differences in ToM, while controlling for other neurocognitive functions.
Results: Compared with controls, patients with schizophrenia and their unaffected siblings performed poorer on the Faux Pas Task (p<0.001), with siblings having intermediate performance between patients and controls. Patients with schizophrenia performed worse than controls on second-order affective condition of the Yoni Task (p=0.004), but their unaffected siblings did not (p=0.063). We did not find any significant Group-by-Condition interaction in the Yoni Task (p=0.358).
Conclusion: Patients with first-episode schizophrenia and their unaffected siblings exhibit ToM impairments, but no dissociation between affective and cognitive component of ToM was found. Our findings support the notion that ToM deficit may be a trait marker of schizophrenia.
Keywords: Endophenotype; Mentalising; Schizophrenia; Social cognition; Theory of mind; Unaffected relatives of schizophrenia.
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