Epigenetic signatures of intergenerational exposure to violence in three generations of Syrian refugees

Abstract

Maternal trauma influences infant and adult health outcomes and may impact future generations through epigenetic modifications such as DNA methylation (DNAm). Research in humans on the intergenerational epigenetic transmission of trauma effects is limited. In this study, we assessed DNAm signatures of war-related violence by comparing germline, prenatal, and direct exposures to violence across three generations of Syrian refugees. We compared families in which a pregnant grandmother versus a pregnant mother was exposed to violence and included a control group with no exposure to war. We collected buccal swab samples and survey data from mothers and 1-2 children in each of 48 families (n = 131 participants). Based on an epigenome-wide association study (EWAS), we identified differentially methylated regions (DMPs): 14 were associated with germline and 21 with direct exposure to violence. Most DMPs showed the same directionality in DNAm change across germline, prenatal, and direct exposures, suggesting a common epigenetic response to violence. Additionally, we identified epigenetic age acceleration in association with prenatal exposure to violence in children, highlighting the critical period of in utero development. This is the first report of an intergenerational epigenetic signature of violence, which has important implications for understanding the inheritance of trauma.

Keywords: DNA methylation; Epigenetic age acceleration; Germline exposure; Maternal trauma; Prenatal exposure.

Fig. 1

Three-generation study design. (a) Our research strategy was designed to test contrasting exposures to violence (direct, prenatal, germline) for changes in DNAm in three groups of three-generation Syrian families. The violence exposures of three generations (F1, F2, F3) for each group are indicated—the 1980 group was directly, prenatally, and germline exposed in the F1 generation, the 2011 group was directly and prenatally exposed in the F2 generation, and the Control group was unexposed. Exposure types are color coded: red = direct exposure, green = prenatal exposure, blue = germline exposure, and yellow = no exposure. (b) Description of exposure groups and primary analytic exposure comparisons. Top panel: Average year of birth, type and time of violence exposure, and time of sample collection are shown for each generation in all three groups. Line color corresponds to exposure type: red = direct exposure, green = prenatal exposure, blue = germline exposure, and yellow = no exposure; dotted line indicates time from oocyte to birth, solid line indicates time from birth to present; vertical orange line indicates year of violence exposure, vertical purple line indicates year of sample collection; righthand labels indicate generation within recruited families: F1 = grandmother, F2 = mother, F3 = child. Bottom panel: participant groups included in each EWAS exposure analysis. Label colors correspond to the color legend in (a) and background colors correspond to the background colors in the top panel of (b).

Fig. 2

Genome-wide significant differences in site-specific DNA methylation when comparing violence exposure groups and controls. Forest plots show DNAm levels for loci that reached genome-wide significance (p-value < 6.5 × 10^–8) in both robust regression and GEE EWAS when comparing germline exposure to violence (a,b) and direct exposure to violence (c,d) to controls. Panels (a) and (c) are forest plots of the beta-value differences between all exposures relative to controls for all significant DMPs. The dots indicate the median difference and bars represent the 95% confidence intervals. Panels (b) and (d) are boxplots of the distribution of beta-values by violence exposure category; the middle line indicates the median, the box covers the interquartile range, and dots indicate observed beta-values. Exposure types are color coded: red = direct exposure, green = prenatal exposure, blue = germline exposure, and yellow = no exposure.

Fig. 3.

DNAm levels and violence trauma exposure scores. Plots show DNAm levels (Y axis) for individual Trauma Event scores (X axis) for (a) 14 germline exposure DMPs and (b) 21 direct exposure DMPs. Black lines are regression lines for all points and gray shading corresponds to 95% confidence intervals.

Fig. 4

Epigenetic age acceleration and violence exposure. (A) Forest plots show differences in epigenetic age acceleration among those exposed to violence relative to controls, comparing the analyses of F2 + F3 (mothers and children) and F3 (children). (B) Boxplots of the distribution of epigenetic age acceleration (residual variation independent of chronological age) by violence exposure category in F3/children. The middle line indicates the median, the box covers the interquartile range, and dots indicate observed Age Acceleration values.