Evidence That the Impact of Childhood Trauma on IQ Is Substantial in Controls, Moderate in Siblings, and Absent in Patients With Psychotic Disorder

Research suggests that childhood trauma is associated with cognitive alterations, but it is not known whether the cognitive alterations observed in patients with psychotic disorder, and their relatives, is trauma-related. Patients with a schizophrenia-spectrum diagnosis (n = 1119), siblings of patients (n = 1059) and healthy comparison subjects (HCS; n = 586) were interviewed 3 times over a period of 6 years. Repeated measures of IQ were analyzed as a function of childhood trauma and group, controlling for confounders. There were significant differences in the impact of childhood trauma on IQ across the 3 groups. Exposure in HCS was associated with a nearly 5-point reduction in IQ (-4.85; 95% confidence interval [CI]: -7.98 to -1.73, P = .002), a lesser reduction in siblings (-2.58; 95% CI: -4.69 to -0.46, P = .017) and no significant reduction in patients (-0.84; 95% CI: -2.78 to 1.10, P = .398). One-fourth of the sibling-control difference in IQ was reducible to childhood trauma, whereas for patients this was only 5%. Over the 6-year follow-up, those with trauma exposure showed significantly less learning effects with repeated cognitive assessments (b = 1.36, 95% CI: 0.80‒1.92, P < .001) than the nonexposed (b = 2.31, 95% CI: 1.92‒2.71, P < .001; P interaction = .001). Although childhood trauma impacts cognitive ability and learning in non-ill people at low and high genetic risk, its effect on the observed cognitive alterations in psychotic disorder may be minor. Twin and family studies on cognitive alterations in psychotic disorder need to take into account the differential impact of trauma on cognition across ill and non-ill, at risk groups.