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Background:The integrity of connections between the hippocampus and the anterior cingulate cortex (ACC) is critical for adaptive cognitive and emotional processing; these connections may be compromised in posttraumatic stress disorder (PTSD). However, there is a lack of PTSD research that combines structural and functional connectivity data, and no studies have examined whether abnormal ACC–hippocampal connectivity is associated with genetic variability, particularly for polymorphisms of a gene that has been previously associated with PTSD, FKBP5. This was the goal of the present study.Methods:Fifty-four women with and without PTSD underwent diffusion tensor imaging and resting-state MRI. Probabilistic tractography was used to examine ACC–hippocampal structural connectivity; mean fractional anisotropy (FA) values were extracted from connectivity streamlines, which represent the cingulum bundle. Genotype data were collected for a single nucleotide polymorphism (SNP) of FKBP5, rs1360780.Results:Participants with PTSD demonstrated poorer structural connectivity (lower cingulum FA) compared to traumatized controls (F1, 50 = 6.77, P < .05). An interaction of FKBP5 genotype and diagnostic group was also observed (F1, 37 = 4.52, P = .04), indicating lower cingulum FA in carriers of two risk alleles for this SNP, compared to other diagnostic and genotype groups. Carriers of two FKBP5 risk alleles also demonstrated poorer hippocampus–ACC connectivity at rest (P < .05). When cingulum FA was used a regressor in a brain-wide, seed-based regression analysis, significant associations were found between the hippocampus and dorsal regions of the ACC (P < .05).Conclusions:Individuals with PTSD demonstrated compromised structural connectivity of the hippocampus–ACC pathway. Altered hippocampus–ACC connectivity may represent a highly salient intermediate neural phenotype for PTSD.

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