GWAS statistical analysis

Genetic analysis was conducted on 7,009,929 SNPs in the European ancestry (EA) sample and 13,862,444 SNPs in the African ancestry sample by the generalized disequilibrium test (GDT) method [45] using family-based information. Principal components (PCs) derived from GWAS data were used to assign ancestry in the genotyped sample, and families were classified as EA or AA according to the ancestry of the greatest proportion of family members. Analyses were conducted separately in the families of AA and EA, using identical phenotypic definitions, covariates, SNP QC standards, MAF thresholds and imputation protocols. Sex, age, the first three PCs (PC1-PC3) computed from SNPRelate, and genotype array were included as covariates. Subsequently, meta-analysis across the EA and AA samples was performed using inverse-variance weighting and genomic control in METAL [46]. Established thresholds for genome-wide significance (p < 5 × 10⁻⁸) were used. We performed MAGMA [47] competitive gene-set analyses using the summary statistics from the GWAS of PTSD in EA and AA individuals using FUMA v1.3.6a (Functional Mapping and Annotation of Genome-Wide Association Studies) [48]. The Genotype-Tissue Expression (GTEx v8 [49]) database was used to obtain gene expression levels in 10 different brain regions.