The role of genes in defining a molecular biology of PTSD.

Because environmental exposure to trauma is the sine qua non for the development of Post Traumatic Stress Disorder (PTSD), the recent focus on genetic studies has been noteworthy. The main catalyst for such studies is the observation from epidemiological studies that not all trauma survivors develop this disorder. Furthermore, neuroendocrine findings suggest pre-existing hormonal alterations that confer risk for PTSD. This paper presents the rationale for examining genetic factors in PTSD and trauma exposure, but suggests that studies of genotype may only present a limited picture of the molecular biology of this disorder. We describe the type of information that can be obtained from candidate gene and genomic studies that incorporate environmental factors in the design (i.e., gene - environment interaction and gene-environment correlation studies) and studies that capitalize on the idea that environment modifies gene expression, via epigenetic or other molecular mechanisms. The examination of epigenetic mechanisms in tandem with gene expression will help refine models that explain how PTSD risk, pathophysiology, and recovery is mediated by the environment. Since inherited genetic variation may also influence the extent of epigenetic or gene expression changes resulting from the environment, such studies should optimally be followed up by studies of genotype.