Although the fact that genetic predisposition and environmental exposures interact to shape development and function of the human brain and, ultimately, the risk of psychiatric disorders has drawn wide interest, the corresponding molecular mechanisms have not yet been elucidated. We found that a functional polymorphism altering chromatin interaction between the transcription start site and long-range enhancers in the FK506 binding protein 5 (FKBP5) gene, an important regulator of the stress hormone system, increased the risk of developing stress-related psychiatric disorders in adulthood by allele-specific, childhood trauma–dependent DNA demethylation in functional glucocorticoid response elements of FKBP5. This demethylation was linked to increased stress-dependent gene transcription followed by a long-term dysregulation of the stress hormone system and a global effect on the function of immune cells and brain areas associated with stress regulation. This identification of molecular mechanisms of genotype-directed long-term environmental reactivity will be useful for designing more effective treatment strategies for stress-related disorders.

OSTTRAUMATIC STRESS DISORder (PTSD) is a debilitating stress-related psychiatric disorder, with prevalence rates of at least 7% to 8% in the US population, and with much higher rates among combat veterans and those living in high-violence areas. 1-3 Initially viewed as a potentially normative response to traumatic exposure, 4 it became clear that not everyone experiencing trauma develops PTSD. Thus, a central question in research on PTSD is why some individuals are more likely than others to develop the disorder in the face of similar levels of trauma exposure. 5-8 Although PTSD is the single disorder within the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) (DSM-IV) 9 that requires a specific environmental insult within its diagnostic criteria, it is becoming increasingly clear that there are critical roles for predisposing genetic and environmental influences in differentially mediating psychological risk to the traumatized individual. 10-13

Pituitary adenylate cyclase-activating polypeptide (PACAP) is known to broadly regulate the cellular stress response. In contrast, it is unclear if the PACAP/PAC1 receptor pathway has a role in human psychological stress responses, such as posttraumatic stress disorder (PTSD). In heavily traumatized subjects, we find a sex-specific association of PACAP blood levels with fear physiology, PTSD diagnosis and symptoms in females (N=64, replication N=74, p<0.005). Using a tag-SNP genetic approach (44 single nucleotide polymorphisms, SNPs) spanning the PACAP (ADCYAP1) and PAC1 (ADCYAP1R1) genes, we find a sex-specific association with PTSD. rs2267735, a SNP in a putative estrogen response element within ADCYAP1R1, predicts PTSD diagnosis and symptoms in females only (combined initial and replication samples: N=1237; p<2x10−5). This SNP also associates with fear discrimination and with ADCYAP1R1 mRNA expression. Methylation of ADCYAP1R1 is also associated with PTSD (p < 0.001). Complementing these human data, ADCYAP1R1 mRNA is induced with fear conditioning or estrogen replacement in rodent models. These data suggest that perturbations in the PACAP/PAC1 pathway are involved in abnormal stress responses underlying PTSD. These sex-specific effects may occur via estrogen regulation of ADCYAP1R1. PACAP levels and ADCYAP1R1 SNPs may serve as useful biomarkers to further our mechanistic understanding of PTSD.

Childhood maltreatment is likely to influence fundamental biological processes and engrave long-lasting epigenetic marks, leading to adverse health outcomes in adulthood. We aimed to elucidate the impact of different early environment on disease-related genomewide gene expression and DNA methylation in peripheral blood cells in patients with posttraumatic stress disorder (PTSD). Compared with the same trauma-exposed controls (n = 108), geneexpression profiles of PTSD patients with similar clinical symptoms and matched adult trauma exposure but different childhood adverse events (n = 32 and 29) were almost completely nonoverlapping (98%). These differences on the level of individual transcripts were paralleled by the enrichment of several distinct biological networks between the groups. Moreover, these gene-expression changes were accompanied and likely mediated by changes in DNA methylation in the same loci to a much larger proportion in the childhood abuse (69%) vs. the non-child abuse-only group (34%). This study is unique in providing genome-wide evidence of distinct biological modifications in PTSD in the presence or absence of exposure to childhood abuse. The findings that nonoverlapping biological pathways seem to be affected in the two PTSD groups and that changes in DNA methylation appear to have a much greater impact in the childhood-abuse group might reflect differences in the pathophysiology of PTSD, in dependence of exposure to childhood maltreatment. These results contribute to a better understanding of the extent of influence of differences in trauma exposure on pathophysiological processes in stress-related psychiatric disorders and may have implications for personalized medicine.hildhood maltreatment is a complex problem that exerts an enormous impact on individuals, families, and society, and is of great significance for public health. Maltreatment during childhood likely influences fundamental biological processes and engraves long-lasting epigenetic marks, leading to adverse health outcomes in adulthood (1). Exposure to adverse life events in childhood has not only been linked to an increased susceptibility for a number of psychiatric disorders, but also to cardiovascular disease, diabetes, and chronic lung disease, possibly via long-term influences on the immune system (2-9). This finding suggests that early adverse experiences not only alter neurobiological systems leading to an increased risk for psychiatric disorders, but may have a long-lasting effect on a number of organ systems. Experience of childhood abuse might influence these biological systems via epigenetic modifications conferring lifelong susceptibility to disease. In fact, in humans, distinct epigenetic and gene-expression changes have been observed in postmortem brains of suicide victims with a history of childhood abuse compared with suicide victims without a history of childhood abuse or control subjects (10).Early life trauma is a strong risk factor for stress-related psychiatric disorders, which themselves have been shown ...

DNA methylation has become increasingly recognized in the etiology of psychiatric disorders. Because brain tissue is not accessible in living humans, epigenetic studies are most often conducted in blood. Saliva is often collected for genotyping studies but is rarely used to examine DNA methylation because the proportion of epithelial cells and leukocytes varies extensively between individuals. The goal of this study was to evaluate whether saliva DNA is informative for studies of psychiatric disorders. DNA methylation (HumanMethylation450 BeadChip) was assessed in saliva and blood samples from 64 adult African Americans. Analyses were conducted using linear regression adjusted for appropriate covariates, including estimated cellular proportions. DNA methylation from brain tissues (cerebellum, frontal cortex, entorhinal cortex, and superior temporal gyrus) was obtained from a publically available dataset. Saliva and blood methylation was clearly distinguishable though there was positive correlation overall. There was little correlation in CpG sites within relevant candidate genes. Correlated CpG sites were more likely to occur in areas of low CpG density (i.e., CpG shores and open seas). There was more variability in CpG sites from saliva than blood, which may reflect its heterogeneity. Finally, DNA methylation in saliva appeared more similar to patterns from each of the brain regions examined overall than methylation in blood. Thus, this study provides a framework for using DNA methylation from saliva and suggests that DNA methylation of saliva may offer distinct opportunities for epidemiological and longitudinal studies of psychiatric traits.

DNA methylation may mediate persistent changes in gene function following chronic stress. To examine this hypothesis, we evaluated African American subjects matched by age and sex, and stratified into four groups by post-traumatic stress disorder (PTSD) diagnosis and history of child abuse. Total Life Stress (TLS) was also assessed in all subjects. We evaluated DNA extracted from peripheral blood using the HumanMethylation27 BeadChip and analyzed both global and site-specific methylation. Methylation levels were examined for association with PTSD, child abuse history, and TLS using a linear mixed model adjusted for age, sex, and chip effects. Global methylation was increased in subjects with PTSD. CpG sites in five genes (TPR, CLEC9A, APC5, ANXA2, and TLR8) were differentially methylated in subjects with PTSD. Additionally, a CpG site in NPFFR2 was associated with TLS after adjustment for multiple testing. Notably, many of these genes have been previously associated with inflammation. Given these results and reports of immune dysregulation associated with trauma history, we compared plasma cytokine levels in these subjects and found IL4, IL2, and TNFα levels associated with PTSD, child abuse, and TLS. Together, these results suggest that psychosocial stress may alter global and gene-specific DNA methylation patterns potentially associated with peripheral immune dysregulation. Our results suggest the need for further research on the role of DNA methylation in stress-related illnesses.

DNA methylation is an important epigenetic mechanism that has been linked to complex disease and is of great interest to researchers as a potential link between genome, environment, and disease. As the scale of DNA methylation association studies approaches that of genome-wide association studies (GWAS), issues such as population stratification will need to be addressed. It is well-documented that failure to adjust for population stratification can lead to false positives in genetic association studies, but population stratification is often unaccounted for in DNA methylation studies. Here, we propose several approaches to correct for population stratification using principal components from different subsets of genome-wide methylation data. We first illustrate the potential for confounding due to population stratification by demonstrating widespread associations between DNA methylation and race in 388 individuals (365 African American and 23 Caucasian). We subsequently evaluate the performance of our principal-components approaches and other methods in adjusting for confounding due to population stratification. Our simulations show that 1) all of the methods considered are effective at removing inflation due to population stratification, and 2) maximum power can be obtained with SNP-based principal components, followed by methylation-based principal components, which out-perform both surrogate variable analysis and genomic control. Among our different approaches to computing methylation-based principal components, we find that principal components based on CpG sites chosen for their potential to proxy nearby SNPs can provide a powerful and computationally efficient approach to adjustment for population stratification in DNA methylation studies when genome-wide SNP data are unavailable.

Half of the data points were inadvertently omitted from the published version of Fig. 4a; the statistical analyses in the text and figure legend, however, do refer to the complete data set. The corrected figure is shown here and has been corrected in the online versions of the paper.In addition, we present additional information to clarify two results reported in the Article regarding plasma pituitary adenylate cyclaseactivating polypeptide (PACAP) levels and post-traumatic stress disorder (PTSD) symptom associations. In the Article, we reported replication of the association between PACAP levels and hyperarousal subscale, because this was the most robust association in the initial cohort. We now present the analyses separately for initial, replication and combined cohorts in Table 1. All associations but one are significant in the replication cohort. The second issue concerns potential medical confounds that could underlie the reported association. Although we do not have medical chart data on most patients, we do have responses from a health questionnaire administered during collection of trauma history and other data. We have now reanalysed the associations for the PTSD symptom scale (PSS) hyperarousal and total symptoms using subjective reports of health condition from the questionnaires as covariates. These data are presented in Table 2 and do not show any effect of health-and illness-related questions on the relationship between PACAP and PTSD symptoms. None of these additions affect the results and conclusions of the original Article.