Extended Swedish Adoption Study of Adverse Stress Responses and Posttraumatic Stress Disorder

Abstract

Twin studies have found that posttraumatic stress disorder (PTSD) is influenced by both genetic and environmental factors within a generation. No study has used an adoption design, which can address questions about the degree and sources of cross-generational transmission of adverse stress responses (ASRs) and PTSD. To examine whether ASRs or PTSD are transmitted from parents to offspring, and to clarify the relative importance of genes and rearing. This cohort study used nationwide Swedish registry data from parents and offspring (n = 2 194 171, born 1960-1992) of 6 types of families (intact; had not lived with biological father; had not lived with biological mother; lived with stepfather; lived with stepmother; and adoptive). Follow-up occurred on December 31, 2018, and data were analyzed from March 3, 2023, to January 16, 2024. Three sources of parent-offspring resemblance: genes plus rearing, genes only, and rearing only. Diagnoses of ASRs or PTSD were obtained from national inpatient, outpatient, and primary care medical registries. Parent-child resemblance was assessed by tetrachoric correlation. Sensitivity analyses were conducted to control for possible shared traumatic events. The study population included 2 194 171 individuals of 6 family types (1 146 703 [52.3%] male; median [range] age, 42 [20-63] years). The weighted tetrachoric correlations across family types were 0.15 (95% CI, 0.15-0.16) for genes plus rearing, 0.08 (95% CI, 0.06-0.11) for genes only, and 0.10 (95% CI, 0.07-0.12) for rearing only. Controlling for potential shared traumatic events, sensitivity analyses found that the correlation for rearing decreased, with the most conservative control (exclusion of parent-offspring dyads with onset of ASRs or PTSD within 1 year) suggesting equal correlations with genes and rearing. Diagnosis of ASRs or PTSD demonstrated cross-generational transmission, including both genetic and rearing correlations. Sensitivity analyses suggested that shared traumatic events partially accounted for the observed rearing correlations.