The Pruning-Vulnerability Cascade in PTSD: Convergent Evidence for Developmental Synaptic and Myelin Dysregulation

Post-traumatic stress disorder (PTSD) has long been understood as an adult-onset disorder of fear extinction and HPA-axis dysregulation, with genetic risk attributed mainly to variants affecting glutamate signalling and stress reactivity. Recent large-scale genome-wide association studies, however, have revealed prominent signals in genes governing synaptic pruning and neuro-immune regulation during brain development. Here we re-analysed the European-ancestry PTSD GWAS summary statistics (effective N = 638,463; Nievergelt et al., 2024) using three orthogonal post-GWAS methods—MAGMA gene-set enrichment, LDSC partitioned heritability (one-tailed jackknife), and S-PrediXcan transcriptome-wide association in six fear-relevant brain regions—applied to both hypothesis-driven custom pruning lists and 13 fully standardised public gene sets (GO, KEGG, Reactome, adult cell-type markers, HGNC HLA). We found robust, replicable enrichment across methods and gene-set sources in the MHC class I histocompatibility complex, complement regulators (especially C4A), adult oligodendrocyte markers, and broad synaptic plasticity pathways. Directionally coherent TWAS signals included upregulation of C4A (Z = +5.28 in frontal cortex) and telomere-maintenance genes (e.g., PPP6C Z = +6.27 in hippocampus), alongside mixed effects in HLA and glutamate-related loci (GRIA1 up, DRD2 down). Negative-control sets were uniformly null. These convergent findings support a refined “pruning-vulnerability cascade”: genetically driven mis-pruning during sensitive developmental windows (Phase 1) leaves corticolimbic and white-matter circuits immature; trauma later overwhelms this fragile scaffold, triggering plasticity failure (Phase 2); and epigenetic consolidation via telomere/senescence pathways locks in the phenotype (Phase 3). The model unifies pre-trauma structural anomalies, early-adversity risk, and genetic overlap with schizophrenia, while highlighting prevention opportunities such as complement-modulating agents in trauma-exposed youth with high HLA/C4A/oligodendrocyte polygenic scores. Broad multi-omic studies in diverse cohorts are now needed to translate this framework into clinical advances.