Background
Offspring to patients with schizophrenia exhibit poorer school performance compared to offspring of non-schizophrenic parents. We aimed to elucidate the mechanisms behind this association.
Methods
We linked longitudinal national population registers in Sweden and compared school performance among offspring to schizophrenic parents to offspring of non-schizophrenic parents (N=1,439,215 with final grades from compulsory school 1988–2006). To investigate the mechanisms, we studied offspring to schizophrenic patients and controls within the same extended families. We investigated genetic effects by stratifying analyses of parent-child associations according to genetic relatedness (half-cousins, full cousins, and half-siblings). Environmental effects were investigated by comparing school performance of offspring to schizophrenic fathers and to schizophrenic mothers, respectively, and by stratifying the analyses according to environmental relatedness while controlling genetic relatedness (paternal and maternal half-cousins, paternal and maternal half-siblings).
Results
Offspring to parents with schizophrenia had poorer overall school performance than unrelated offspring to non-schizophrenic parents (−0.31 SD). Variability in genetic relatedness greatly moderated the strength of the within-family association (β=−0.23 within exposure-discordant half-cousins, β=−0.13 within exposure-discordant full cousins, and β=0.04 within exposure-discordant half-siblings), while no evidence was found that the environment affected offspring school performance.
Conclusions
Genetic factors account for poorer school performance in children of parents with schizophrenia. This supports that cognitive deficits found in individuals with schizophrenia and their relatives might be genetically inherited. Early detection of prodromal signs and impaired functioning of offspring to patients with schizophrenia could lead to earlier and better tailored interventions.