The SNP most strongly associated (Table 2) with PTSD is rs12364283 [OR 1.65 (1.27–2.15); unadjusted p= 1.58 × 10−4], a functional DRD2 promoter polymorphism. Consistent with an additive model (see Supplementary Table 3), the prevalence of PTSD increases with the number of G allele copies: 35.6% (0 copies); 45.6% (1 copy); 70.0% (2 copies). However, the relatively low minor allele frequency (7.7%) precludes definitive determination of mode of inheritance. The association observed for rs12805897 is likely due to its high linkage disequilibrium with rs12364283 (r2=.96). The only other SNP with an association within an order of magnitude of the strongest observed signal is rs10840491 located in the tyrosine hydroxylase (TH) gene. Although the associations of these additional SNPs are of considerably lower magnitude, it is interesting to note that included among them are polymorphisms from genes encoding dopamine (DA) receptors (DRD2, DRD3), an enzyme (TH) involved in DA synthesis, and an enzyme (DBH) that converts DA to norepinephrine.
