The environment contributes more than genetics to smaller hippocampal volume in Posttraumatic Stress Disorder (PTSD).
Level 4 - case-series / case-control
Co-twin case-control study
PubMed 33168198 · doi:10.1016/j.jpsychires.2020.10.042
What was done
Structural MRI was used to measure hippocampal volume in a co-twin case-control study of Vietnam-era military veteran twin pairs discordant for combat deployment and PTSD. The sample included 13 monozygotic pairs and 21 dizygotic pairs (34 pairs, 68 individuals total), where one brother served in Vietnam and developed PTSD and the other did not deploy or develop PTSD. Left and right hippocampal volumes were determined by manual tracing across coronal slices adjusted for slice thickness.
What was found
Twins with combat-related PTSD had a statistically significant mean 11% smaller right hippocampal volume compared with their non-deployed, non-PTSD co-twins (p < .05). There was no significant interaction by zygosity. Absolute volumetric values and specific findings for the left hippocampus were not reported in the abstract.
Why it matters
Using a discordant twin design, this study provides evidence that reduced right hippocampal volume in PTSD reflects environmental stress exposure rather than pre-existing genetic vulnerability.
Limits
The sample size was small (particularly 13 monozygotic pairs), limiting statistical power. The study included only male Vietnam-era veterans, so findings may not generalize to other trauma types or female populations. Pre-trauma baseline hippocampal volumes were not available, and left hippocampal results were omitted from the abstract.
Cited by
- supports MRIs of soldiers returning from war demonstrate degeneration of the hippocampus.