EXPLORING THE IMMUNOGENETIC BASIS OF POST-TRAUMATIC STRESS DISORDER

Abstract

Post-Traumatic Stress Disorder (PTSD) is a complex psychiatric condition that develops following exposure to traumatic experiences. Its core symptoms include intrusive thoughts, avoidant behavior, and a persistent state of hyperarousal. Although it is widely recognized that stress exacerbates inflammation across tissues, a growing body of evidence suggests a reciprocal relationship, with immune function influencing susceptibility to PTSD. This relationship may be driven by shared underlying biology, such as from pleiotropy. The most recent genome-wide association study (GWAS) of PTSD identified 95 risk loci, including endocrine and immune regulators, such as the major histocompatibility complex (MHC). The MHC harbors numerous genetic variants such as human leukocyte antigen (HLA) alleles that are crucial for immune function. However, the complex linkage disequilibrium structure of the MHC poses challenges in isolating individual signals through SNP-based imputation. Here, we present a large-scale cross-ancestry analysis assessing the association of HLA alleles with PTSD.

We conducted HLA imputation and association analysis in a genotyped sample of individuals of African, European, or Latin American ancestry from 38 studies included in the latest PTSD GWAS published by the Psychiatric Genomics Consortium. The outcome phenotype was assessed as either case-control or on a continuous scale (e.g. the PTSD Checklist for DSM-IV or V). The 1000 Genomes Reference Panel, comprised of individuals from African, East Asian, European, South Asian, and American populations was employed to impute around 350 HLA alleles via SHAPEIT5 and MINIMAC4. Additionally, we introduced 21 long-range HLA haplotypes into the reference. Regression analyses were conducted using PLINK 2.0, while the first five principal components were included as covariates to adjust for population stratification. Finally, we employed METAL, using the sample-size weighting approach, to meta-analyze results from dichotomous and continuous outcomes.

We have generated preliminary results in a multi-ancestry sample (N = 60,159) that highlight HLA-DRB1*01:01 as the top risk-conferring allele across three ancestries (Z = 3.255, P = 1.14e-03). HLA-DRB1*01:01 was also the most significant HLA allele (Z = 2.380, P = 1.73e-02) in the Latin American sample (n = 7,072). In the African sample (n = 14,883), HLA-B*51:01 (Z = 3.553, P = 3.82e-04) emerged as the most significant HLA allele, while in Europeans (n = 38,204), the most significant allele HLA-B*08:01 showed a negative association with PTSD (Z = -2.555, P = 1.06e-02).

Our association analysis has identified multiple HLA alleles nominally associated with PTSD, with HLA-DRB1*01:01 emerging as the most significant possibly risk-conferring variant across ancestries. Notably, a protective effect of HLA-B*08:01 has previously been observed in schizophrenia and bipolar disorder. In the next steps, we will conduct imputation and association analyses for complement component 4, located in the MHC class III region, and perform conditional analyses to pinpoint independent effects. Finally, we aim to incorporate additional large-scale samples such as the Million Veteran Program and the UK Biobank to increase statistical power.