Development of social responsiveness and theory of mind in children of parents with schizophrenia or bipolar disorder.

Social impairments are suggested as vulnerability markers for schizophrenia and bipolar disorder. Therefore, we investigated the development of social responsiveness and theory of mind (ToM) in children at familial high-risk of schizophrenia (FHR-SZ) or bipolar disorder (FHR-BP). This study is part of The Danish High Risk and Resilience Study, a longitudinal cohort study of children at FHR-SZ or FHR-BP and population-based controls (PBC). Social responsiveness was measured with the Social Responsiveness Scale (SRS-2), completed by teachers and primary caregivers. ToM was measured using The Animated Triangles Task (ATT). Both SRS-2 and ATT were applied at age 7 and 11. A total of 520 children participated (FHR-SZ,  = 201; FHR-BP,  = 119; PBC,  = 200). Results showed no significant time by group interactions. At follow-up, children at FHR-SZ exhibited impaired social responsiveness compared with PBC regardless of the informant. At both timepoints, a higher proportion of children at FHR-SZ were rated at a clinically significant level, implying inference in everyday social interactions. Compared with PBC, primary caregivers reported impairments in social responsiveness in children at FHR-BP at follow-up. The three groups did not differ in ToM at follow-up. Social responsiveness and ToM do not develop differently in children at FHR-SZ, FHR-BP and PBC from age 7 to 11, but impairments in social responsiveness remain stable and may constitute a vulnerability marker particularly in children at FHR-SZ, but also FHR-BP. ToM abilities seem to improve and remain intact, but ToM development and ToM task properties should be taken into consideration.