Gene-environment interaction of ApoE genotype and combat exposure on PTSD

Brain reserve in midlife is associated with executive function changes across 12 years

We examined how brain reserve in midlife, measured by brain-predicted age difference scores (Brain-PADs), predicted executive function concurrently and longitudinally into early old age, and whether these associations were moderated by young adult cognitive reserve or APOE genotype. 508 men in the Vietnam Era Twin Study of Aging (VETSA) completed neuroimaging assessments at mean age 56 and six executive function tasks at mean ages 56, 62, and 68 years. Results indicated that greater brain reserve at age 56 was associated with better concurrent executive function (r=.10, p=.040) and less decline in executive function over 12 years (r=.34, p=.001). These associations were not moderated by cognitive reserve or APOE genotype. Twin analysis suggested associations with executive function slopes were driven by genetic influences. Our findings suggest that greater brain reserve allowed for better cognitive maintenance from middle- to old age, driven by a genetic association. The results are consistent with differential preservation of executive function based on brain reserve that is independent of young adult cognitive reserve or APOE genotype.

No Replication of Alzheimer's Disease Genetics as a Moderator of Combat Exposure's Association with PTSD risk in 138,592 Combat Veterans

Large-scale cohort and epidemiological studies suggest that posttraumatic stress disorder (PTSD) confers risk for late-onset Alzheimer's disease (AD) and related dementias (ADRD); however, the basis for this association remains unclear. Several prior studies of military Veterans have reported that carriers of the apolipoprotein E (APOE) ε4 gene variant are at heightened risk for the development of PTSD following combat exposure, suggesting that PTSD and ADRD may share some genetic risk. This cohort study was designed to further examine the hypothesis that ADRD genetic risk also confers risk for PTSD. To do so, we examined APOE ε4 and ε2 genotypes, an AD polygenic risk score (PRS), and other Veteran-relevant risk factors for PTSD in age-stratified groups of individuals of European (n = 123,372) and African (n = 15,220) ancestry in the US Department of Veterans Affairs' Million Veteran Program. Analyses revealed no significant main effect associations between the APOE ε4 (or ε2) genotype or the AD PRS on PTSD severity or diagnosis. There were also no significant interactions between measures of AD genetic risk and either combat exposure severity or history of head injury in association with PTSD in any age group. We conclude that the association between PTSD and the primary ADRD genetic risk factor, APOE ε4, that was reported previously was not replicable in the largest relevant dataset in the world. Thus, the epidemiological association between PTSD and ADRD is not likely to be driven by the major genetic factors underlying ADRD risk.

Assessment of the Genetic Characteristics of a Generation Born during a Long-Term Socioeconomic Crisis

BACKGROUND

A socioeconomic crisis in Russia lasted from 1991 to 1998 and was accompanied by a sharp drop in the birth rate. The main factor that influenced the refusal to have children during this period is thought to be prolonged social stress.

METHODS

comparing frequencies of common gene variants associated with stress-induced diseases among generations born before, after, and during this crisis may show which genes may be preferred under the pressure of natural selection during periods of increased social stress in urban populations.

RESULTS

In the "crisis" group, a statistically significant difference from the other two groups was found in rs6557168 frequency (p = 0.001); rs4522666 was not in the Hardy-Weinberg equilibrium in this group, although its frequency did not show a significant difference from the other groups (p = 0.118). Frequencies of VNTRs in SLC6A3 and MAOA as well as common variants rs17689918 in CRHR1, rs1360780 in FKBP5, rs53576 in OXTR, rs12720071 and rs806377 in CNR1, rs4311 in ACE, rs1800497 in ANKK1, and rs7412 and rs429358 in APOE did not differ among the groups.

CONCLUSIONS

a generation born during a period of prolonged destructive events may differ from the rest of the gene pool of the population in some variants associated with personality traits or stress-related disorders.

Trauma Matters: Integrating Genetic and Environmental Components of PTSD

Trauma is ubiquitous, but only a subset of those who experience trauma will develop posttraumatic stress disorder (PTSD). In this review, it is argued that to determine who is at risk of developing PTSD, it is critical to examine the genetic etiology of the disorder and individual trauma profiles of those who are susceptible. First, the state of current PTSD genetic research is described, with a particular focus on studies that present evidence for trauma type specificity, or for differential genetic etiology according to gender or race. Next, approaches that leverage non-traditional phenotyping approaches are reviewed to identify PTSD-associated variants and biology, and the relative advantages and limitations inherent in these studies are reflected on. Finally, it is discussed how trauma might influence the heritability of PTSD, through type, risk factors, genetics, and associations with PTSD symptomology.

Alzheimer's disease and related dementias among aging veterans: Examining gene-by-environment interactions with post-traumatic stress disorder and traumatic brain injury

INTRODUCTION

Post-traumatic stress disorder (PTSD) and traumatic brain injury (TBI) confer risk for Alzheimer's disease and related dementias (ADRD).

METHODS

This study from the Million Veteran Program (MVP) evaluated the impact of apolipoprotein E (APOE) ε4, PTSD, and TBI on ADRD prevalence in veteran cohorts of European ancestry (EA; n = 11,112 ADRD cases, 170,361 controls) and African ancestry (AA; n = 1443 ADRD cases, 16,191 controls). Additive-scale interactions were estimated using the relative excess risk due to interaction (RERI) statistic.

RESULTS

PTSD, TBI, and APOE ε4 showed strong main-effect associations with ADRD. RERI analysis revealed significant additive APOE ε4 interactions with PTSD and TBI in the EA cohort and TBI in the AA cohort. These additive interactions indicate that ADRD prevalence associated with PTSD and TBI increased with the number of inherited APOE ε4 alleles.

DISCUSSION

PTSD and TBI history will be an important part of interpreting the results of ADRD genetic testing and doing accurate ADRD risk assessment.

Alzheimer's Disease Polygenic Scores Predict Changes in Episodic Memory and Executive Function Across 12 Years in Late Middle Age

OBJECTIVE

Alzheimer's disease (AD) is highly heritable, and AD polygenic risk scores (AD-PRSs) have been derived from genome-wide association studies. However, the nature of genetic influences very early in the disease process is still not well known. Here we tested the hypothesis that an AD-PRSs would be associated with changes in episodic memory and executive function across late midlife in men who were cognitively unimpaired at their baseline midlife assessment..

METHOD

We examined 1168 men in the Vietnam Era Twin Study of Aging (VETSA) who were cognitively normal (CN) at their first of up to three assessments across 12 years (mean ages 56, 62, and 68). Latent growth models of episodic memory and executive function were based on 6-7 tests/subtests. AD-PRSs were based on Kunkle et al. (Nature Genetics, 51, 414-430, 2019), p < 5×10^-8 threshold.

RESULTS

AD-PRSs were correlated with linear slopes of change for both cognitive abilities. Men with higher AD-PRSs had steeper declines in both memory (r = -.19, 95% CI [-.35, -.03]) and executive functioning (r = -.27, 95% CI [-.49, -.05]). Associations appeared driven by a combination of APOE and non-APOE genetic influences.

CONCLUSIONS

Memory is most characteristically impaired in AD, but executive functions are one of the first cognitive abilities to decline in midlife in normal aging. This study is among the first to demonstrate that this early decline also relates to AD genetic influences, even in men CN at baseline.

Associations Between Ambient Air Pollution and Cognitive Abilities from Midlife to Early Old Age: Modification by APOE Genotype

BACKGROUND

Fine particulate matter (PM2.5) and nitrogen dioxide (NO2) measures of ambient air pollution are associated with accelerated age-related cognitive impairment, and Alzheimer's disease and related dementias (ADRD).

OBJECTIVE

We examined associations between air pollution, four cognitive factors, and the moderating role of apolipoprotein E (APOE) genotype in the understudied period of midlife.

METHODS

Participants were ∼1,100 men in the Vietnam Era Twin Study of Aging. Baseline cognitive assessments were from 2003 to 2007. Measures included past (1993-1999) and recent (3 years prior to baseline assessment) PM2.5 and NO2 exposure, in-person assessment of episodic memory, executive function, verbal fluency, and processing speed, and APOE genotype. Average baseline age was 56 years with a 12-year follow-up. Analyses adjusted for health and lifestyle covariates.

RESULTS

Performance in all cognitive domains declined from age 56 to 68. Higher PM2.5 exposures were associated with worse general verbal fluency. We found significant exposure-by-APOE genotype interactions for specific cognitive domains: PM2.5 with executive function and NO2 with episodic memory. Higher PM2.5 exposure was related to worse executive function in APOE ɛ4 carriers, but not in non-carriers. There were no associations with processing speed.

CONCLUSION

These results indicate negative effects of ambient air pollution exposure on fluency alongside intriguing differential modifications of cognitive performance by APOE genotype. APOE ɛ4 carriers appeared more sensitive to environmental differences. The process by which air pollution and its interaction with genetic risk for ADRD affects risk for later life cognitive decline or progression to dementia may begin in midlife.

Genetic Variants Associated With Resilience in Human and Animal Studies

Resilience is broadly defined as the ability to maintain or regain functioning in the face of adversity and is influenced by both environmental and genetic factors. The identification of specific genetic factors and their biological pathways underpinning resilient functioning can help in the identification of common key factors, but heterogeneities in the operationalisation of resilience have hampered advances. We conducted a systematic review of genetic variants associated with resilience to enable the identification of general resilience mechanisms. We adopted broad inclusion criteria for the definition of resilience to capture both human and animal model studies, which use a wide range of resilience definitions and measure very different outcomes. Analyzing 158 studies, we found 71 candidate genes associated with resilience. OPRM1 (Opioid receptor mu 1), NPY (neuropeptide Y), CACNA1C (calcium voltage-gated channel subunit alpha1 C), DCC (deleted in colorectal carcinoma), and FKBP5 (FKBP prolyl isomerase 5) had both animal and human variants associated with resilience, supporting the idea of shared biological pathways. Further, for OPRM1, OXTR (oxytocin receptor), CRHR1 (corticotropin-releasing hormone receptor 1), COMT (catechol-O-methyltransferase), BDNF (brain-derived neurotrophic factor), APOE (apolipoprotein E), and SLC6A4 (solute carrier family 6 member 4), the same allele was associated with resilience across divergent resilience definitions, which suggests these genes may therefore provide a starting point for further research examining commonality in resilience pathways.

Apolipoprotein E Isoform-specific changes related to stress and trauma exposure

Post-Traumatic Stress Disorder (PTSD) is a highly prevalent mental health disorder. Due to the high level of variability in susceptibility and severity, PTSD therapies are still insufficient. In addition to environmental exposures, genetic risks play a prominent role and one such factor is apolipoprotein E. The protein (apoE) is functionally involved in cholesterol transport and metabolism and exists as 3 major isoforms in humans: E2, E3, and E4. To model the role of apolipoprotein E isoform in stress-related changes in behavior and cognition, female and male mice (3-5 months of age) expressing E2, E3, or E4 were used. Mice were either placed into control groups or exposed to chronic variable stress (CVS), which has been shown to induce PTSD-like behavioral and neuroendocrine changes. E2 mice showed a unique response to CVS compared to E3 and E4 mice that included impaired spatial learning and memory, increased adrenal gland weight, and no increase in glucocorticoid receptor protein levels (normalized to apoE levels). In addition, the cholesterol metabolite 7-ketocholesterol was elevated in the cortex after CVS in E3 and E4, but not E2 female mice. E2 confers unique changes in behavioral, cognitive, and biomarker profiles after stress exposure and identify 7-ketocholesterol as a possible novel biomarker of the traumatic stress response. We further explored the relationship between E2 and PTSD in an understudied population by genotyping 102 patients of Cambodian and Vietnamese ethnicity. E2 carriers demonstrated a higher odds ratio of having a PTSD diagnosis compared to E3/E3 carriers, supporting that the E2 genotype is associated with PTSD diagnosis after trauma exposure in this population.

Paradoxical cognitive trajectories in men from earlier to later adulthood

Because longitudinal studies of aging typically lack cognitive data from earlier ages, it is unclear how general cognitive ability (GCA) changes throughout the life course. In 1173 Vietnam Era Twin Study of Aging (VETSA) participants, we assessed young adult GCA at average age 20 and current GCA at 3 VETSA assessments beginning at average age 56. The same GCA index was used throughout. Higher young adult GCA and better GCA maintenance were associated with stronger specific cognitive abilities from age 51 to 73. Given equivalent GCA at age 56, individuals who had higher age 20 GCA outperformed those whose GCA remained stable in terms of memory, executive function, and working memory abilities from age 51 to 73. Thus, paradoxically, despite poorer maintenance of GCA, high young adult GCA still conferred benefits. Advanced predicted brain age and the combination of elevated vascular burden and APOE-ε4 status were associated with poorer maintenance of GCA. These findings highlight the importance of distinguishing between peak and current GCA for greater understanding of cognitive aging.

Apolipoprotein E e4 is associated with worse self-reported neurobehavioral symptoms following uncomplicated mild traumatic brain injury in U.S. military service members

Past research has found a relationship between the apolipoprotein E (APOE) e4 allele and worse neurobehavioral functioning following mild traumatic brain injury (MTBI) in civilian populations. The purpose of this study was to examine this relationship in service members and veterans (SMVs) following MTBI. Participants were 151 SMVs (103 uncomplicated MTBI; 48 Injured Controls [IC]) prospectively enrolled in the DVBIC-TBICoE 15-Year Longitudinal TBI Study. Participants completed a battery of self-reported neurobehavioral symptom measures on average 76.2 months post-injury (SD = 31.8). APOE genotyping was undertaken using non-fasting blood samples. Participants were classified into four subgroups based on injury (MTBI vs. IC) and APOE e4 allele status (e4 present/absent). In the IC group, there were no significant differences across APOE e4 status subgroups for all measures. In the MTBI group, participants with the APOE e4 allele had significantly worse scores on measures of depression, pain, anxiety, grief, positive well-being, social participation, and resilience compared to those without the e4 allele (d = .44 to d = .69). When comparing the number of 'clinically elevated' neurobehavioral measures simultaneously, the MTBI/e4 present subgroup consistently had a higher number of elevated measures compared to the MTBI/e4 absent, IC/e4 present, and IC/e4 absent subgroups. The APOE e4 allele was associated with poorer neurobehavioral outcome in SMVs in the chronic phase of recovery following MTBI. APOE e4 could be incorporated into screening tools to predict SMVs at risk for poor long-term neurobehavioral outcome in an effort to provide early intervention to improve long-term clinical outcome.

Posttraumatic Stress Disorder in the Elderly

Posttraumatic stress disorder (PTSD) can occur at any point in the life span and can last for decades. Chronic PTSD can affect quality of life and have a negative impact on physical function and health in the elderly and may be associated with premature aging and dementia. It is critical that clinicians screen for trauma-based symptoms and to treat as appropriate.

Interaction between Alcohol Consumption and Apolipoprotein E (ApoE) Genotype with Cognition in Middle-Aged Men

OBJECTIVE

Heavy alcohol consumption is associated with poorer cognitive function in older adults. Although understudied in middle-aged adults, the relationship between alcohol and cognition may also be influenced by genetics such as the apolipoprotein (ApoE) ε4 allele, a risk factor for Alzheimer's disease. We examined the relationship between alcohol consumption, ApoE genotype, and cognition in middle-aged adults and hypothesized that light and/or moderate drinkers (≤2 drinks per day) would show better cognitive performance than heavy drinkers or non-drinkers. Additionally, we hypothesized that the association between alcohol use and cognitive function would differ by ApoE genotype (ε4+ vs. ε4-).

METHOD

Participants were 1266 men from the Vietnam Era Twin Study of Aging (VETSA; M age = 56; range 51-60) who completed a neuropsychological battery assessing seven cognitive abilities: general cognitive ability (GCA), episodic memory, processing speed, executive function, abstract reasoning, verbal fluency, and visuospatial ability. Alcohol consumption was categorized into five groups: never, former, light, moderate, and heavy.

RESULTS

In fully adjusted models, there was no significant main effect of alcohol consumption on cognitive functions. However, there was a significant interaction between alcohol consumption and ApoE ε4 status for GCA and episodic memory, such that the relationship of alcohol consumption and cognition was stronger in ε4 carriers. The ε4+ heavy drinking subgroup had the poorest GCA and episodic memory.

CONCLUSIONS

Presence of the ε4 allele may increase vulnerability to the deleterious effects of heavy alcohol consumption. Beneficial effects of light or moderate alcohol consumption were not observed.

Posttraumatic stress symptom persistence across 24 years: association with brain structures

Posttraumatic stress disorder (PTSD) is known to persist, eliciting early medical co-morbidity, and accelerated aging. Although PTSD diagnosis has been found to be associated with smaller volume in multiple brain regions, posttraumatic stress (PTS) symptoms and their associations with brain morphometry are rarely assessed over long periods of time. We predicted that persistent PTS symptoms across ~24 years would be inversely associated with hippocampal, amygdala, anterior cingulate volumes, and hippocampal occupancy (HOC = hippocampal volume/[hippocampal volume + inferior lateral ventricle volume]) in late middle age. Exploratory analyses examined prefrontal regions. We assessed PTS symptoms in 247 men at average ages 38 (time 1) and 62 (time 2). All were trauma-exposed prior to time 1. Brain volumes were assessed at time 2 using 3 T structural magnetic resonance imaging. Symptoms were correlated over time (r = 0.46 p < .0001). Higher PTS symptoms averaged over time and symptoms at time 1 were both associated with lower hippocampal, amygdala, rostral middle frontal gyrus (MFG), and medial orbitofrontal cortex (OFC) volumes, and a lower HOC ratio at time 2. Increased PTS symptomatology from time 1 to time 2 was associated with smaller hippocampal volume. Results for hippocampal, rostral MFG and medial OFC remained significant after omitting individuals above the threshold for PTSD diagnosis. Even at sub-diagnostic threshold levels, PTS symptoms were present decades after trauma exposure in parallel with highly correlated structural deficits in brain regions regulating stress responsivity and adaptation.

Genetic and Environmental Predictors of Adolescent PTSD Symptom Trajectories Following a Natural Disaster

: Genes, environmental factors, and their interplay affect posttrauma symptoms. Although environmental predictors of the longitudinal course of posttraumatic stress disorder (PTSD) symptoms are documented, there remains a need to incorporate genetic risk into these models, especially in youth who are underrepresented in genetic studies. In an epidemiologic sample tornado-exposed adolescents (n = 707, 51% female, Mage = 14.54 years), trajectories of PTSD symptoms were examined at baseline and at 4-months and 12-months following baseline. This study aimed to determine if rare genetic variation in genes previously found in the sample to be related to PTSD diagnosis at baseline (MPHOSPH9, LGALS13, SLC2A2), environmental factors (disaster severity, social support), or their interplay were associated with symptom trajectories. A series of mixed effects models were conducted. Symptoms decreased over the three time points. Elevated tornado severity was associated with elevated baseline symptoms. Elevated recreational support was associated with lower baseline symptoms and attenuated improvement over time. Greater LGLAS13 variants attenuated symptom improvement over time. An interaction between MPHOSPH9 variants and tornado severity was associated with elevated baseline symptoms, but not change over time. Findings suggest the importance of rare genetic variation and environmental factors on the longitudinal course of PTSD symptoms following natural disaster trauma exposure.

Assessing for interaction between APOE ε4, sex, and lifestyle on cognitive abilities

OBJECTIVE

To test for interactions between APOE ε4 genotype and lifestyle factors on worse cognitive abilities in UK Biobank.

METHODS

Using UK Biobank cohort data, we tested for interactions between APOE ε4 allele presence, lifestyle factors of alcohol intake, smoking, total physical activity and obesity, and sex, on cognitive tests of reasoning, information processing speed, and executive function (n range = 70,988-324,725 depending on the test). We statistically adjusted for potential confounders of age, sex, deprivation, cardiometabolic conditions, and educational attainment.

RESULTS

There were significant associations between APOE ε4 and worse cognitive abilities, independent of potential confounders, and between lifestyle risk factors and worse cognitive abilities; however, there were no interactions at multiple correction-adjusted p < 0.05, against our hypotheses.

CONCLUSIONS

Our results do not provide support for the idea that ε4 genotype increases vulnerability to the negative effects of lifestyle risk factors on cognitive ability, but rather support a primarily outright association between APOE ε4 genotype and worse cognitive ability.

Negative fateful life events in midlife and advanced predicted brain aging

Negative fateful life events (FLEs) such as interpersonal conflict, death in the family, financial hardship, and serious medical emergencies can act as allostatic stressors that accelerate biological aging. However, the relationship between FLEs and neuroanatomical aging is not well understood. We examined 359 men (mean age 62 years) participating in the Vietnam Era twin study of aging (VETSA) to determine whether negative midlife FLEs are associated with advanced brain aging after controlling for physical, psychological, and lifestyle factors. At two different time points, participants were assessed for negative FLEs, health and well-being, general cognitive ability, socioeconomic status, depression, and ethnicity. Participants underwent a magnetic resonance imaging examination, and T1-weighted images were processed with FreeSurfer. Subsequent neuroanatomical measurements were entered into the Brain-Age Regression Analysis and Computation Utility software (BARACUS) to predict brain age. Having more midlife FLEs, particularly relating to interpersonal relationships, was associated with advanced predicted brain aging (i.e., higher predicted brain age relative to chronological age). This association remained after controlling for the significant covariates of alcohol consumption, cardiovascular risk, adult socioeconomic status, and ethnicity.

Apolipoprotein E ε4 Genotype Is Associated with Elevated Psychiatric Distress in Veterans with a History of Mild to Moderate Traumatic Brain Injury

As few studies have examined the relationship between the apolipoprotein E (APOE) gene and clinical outcomes after military-related traumatic brain injury (TBI), we aimed to determine whether the ε4 allele of the APOE gene influences neuropsychiatric symptoms in veterans with a history of mild-to-moderate TBI. Participants included 133 veterans (TBI = 79; military controls [MC] = 54) who underwent APOE genotyping and were divided into ε4⁺ (TBI = 18; MC = 15) and ε4^- (TBI = 61; MC = 39) groups. All participants underwent evaluation of psychological distress using the Beck Depression Inventory-II, Beck Anxiety Inventory, and PTSD Checklist-Military Version. Two-way analyses of variance were conducted to examine the effect of group (TBI vs. MC) and APOE-ε4 status (ε4⁺ vs. ε4^-) across symptom measures. There was a significant main effect of group across all symptom measures (TBI > MC; all p values <0.001), no main effect of ε4 genotype (p = 0.152-0.222), and a significant interaction of group by ε4 genotype across all measures (p = 0.027-0.047). Specifically, for TBI participants, ε4⁺ veterans demonstrated significantly higher symptom scores across all measures when compared to ε4^- veterans (p = 0.007-0.015). For MC participants, ε4 status had no effect on the severity of psychiatric symptom scores (p = 0.585-0.708). Our results demonstrate that, in our well-characterized sample of veterans with history of neurotrauma, possession of the ε4 allele conveys risk for increased symptomatology (i.e., depression, anxiety, and post-traumatic stress disorder), even well outside of the acute phase of injury. Findings suggest a meaningful relationship between APOE genotype and psychiatric distress post-TBI, and they suggest that there is a brain basis for the complex neuropsychiatric presentation often observed in this vulnerable population. Future longitudinal studies are needed in order to further our understanding of how genetic factors influence response to TBI.

Apolipoprotein E DNA methylation and posttraumatic stress disorder are associated with plasma ApoE level: A preliminary study

Mild traumatic brain injury (mTBI) occurred in 15-30% of Veterans returning from Iraq and Afghanistan. We examined whether DNA methylation of the apolipoprotein E (APOE) gene promoter region or plasma ApoE protein levels are altered in mTBI. APOE promoter region DNA methylation, APOE genotype, and plasma ApoE concentration were determined in 87 Veterans with or without mTBI who were recruited from 2010-2014. Plasma ApoE concentration was found to be associated with Posttraumatic Stress Disorder (PTSD) symptom severity ratings by hierarchical linear regression (p = .013) and ANCOVA (p = .007). Hierarchical linear regression revealed that plasma ApoE concentration was associated with APOE-ε4 genotype status (p=.022). Higher ApoE plasma levels were found in ε3/ε3 Veterans than in APOE-ε4 carriers (p = .031). Furthermore, plasma ApoE concentration was associated experiment-wise with DNA methylation at CpG sites -877 (p = .021), and -775 (p = .014). The interaction between APOE-ε4 genotype and having a PTSD diagnosis was associated with DNA methylation at CpG site -675 (p = .009).

Pharmacogenetics and Pharmacotherapy of Military Personnel Suffering from Post-traumatic Stress Disorder

Background:

Posttraumatic stress disorder (PTSD) is a severe problem among soldiers with combating experience difficult to treat. The pathogenesis is still not fully understood at the psychological level. Therefore, genetic research became a focus of interest. The identification of single nucleotide polymorphisms (SNPs) may help to predict, which persons are at high risk to develop PTSD as a starting point to develop novel targeted drugs for treatment.

Methods:

We conducted a systematic review on SNPs in genes related to PTSD pathology and development of targeted pharmacological treatment options based on PubMed database searches. We focused on clinical trials with military personnel.

Results:

SNPs in 22 human genes have been linked to PTSD. These genes encode proteins acting as neurotransmitters and receptors, downstream signal transducers and metabolizing enzymes. Pharmacological inhibitors may serve as drug candidates for PTSD treatment, e.g. β2 adrenoreceptor antagonists, dopamine antagonists, partial dopamine D2 receptor agonists, dopamine β hydroxylase inhibitors, fatty acid amid hydrolase antagonists, glucocorticoid receptor agonists, tropomyosin receptor kinase B agonists, selective serotonin reuptake inhibitors, catechol-O-methyltransferase inhibitors, gamma-amino butyric acid receptor agonists, glutamate receptor inhibitors, monoaminoxidase B inhibitors, N-methyl-d-aspartate receptor antagonists.

Conclusion:

The combination of genetic and pharmacological research may lead to novel target-based drug developments with improved specificity and efficacy to treat PTSD. Specific SNPs may be identified as reliable biomarkers to assess individual disease risk. Focusing on soldiers suffering from PTSD will not only help to improve treatment options for this specific group, but for all PTSD patients and the general population.

Posttraumatic Stress Disorder in the Elderly

Posttraumatic stress disorder (PTSD) can occur at any point in the life span and can last for decades. Chronic PTSD can affect quality of life and have a negative impact on physical function and health in the elderly and may be associated with premature aging and dementia. It is critical that clinicians screen for trauma-based symptoms and to treat as appropriate.

Apolipoprotein E gene polymorphism, trauma burden, and posttraumatic stress symptoms in U.S. military veterans: Results from the National Health and Resilience in Veterans Study

BACKGROUND

Previous research examining the association between apolipoprotein E (APOE) gene polymorphism and risk for posttraumatic stress disorder (PTSD) has been inconsistent due to the use of small and select samples. This study examined the relation between APOE genotype and PTSD symptoms in two nationally representative samples of U.S. military veterans. The potential effect of cumulative trauma burden and social support in moderating this association was also evaluated.

METHODS

The main sample consisted of 1,386 trauma-exposed European American (EA) veterans (mean age: 62-63 years) who participated in the National Health and Resilience in Veterans Study (NHRVS) in 2011. The independent replication sample consisted of 509 trauma-exposed EA veterans from the 2013 NHRVS.

RESULTS

APOE ε4 allele carriers reported significantly greater severity of PTSD symptoms than noncarriers in the main, but not the replication, sample. In both samples, the interaction of APOE ε4 carrier status and cumulative trauma burden was associated with greater severity of PTSD symptoms (F range = 2.53-8.09, all P's < .01), particularly re-experiencing/intrusion symptoms (F range = 3.59-4.24, P's < .001). Greater social support was associated with lower severity of PTSD symptoms among APOE ε4 allele carriers with greater cumulative trauma burden (β range -.27 to -.60, P's < .05).

CONCLUSION

U.S. military veterans who are APOE ε4 allele carriers and exposed to a high number of traumas may be at increased risk for developing PTSD symptoms than ε4 noncarriers. Greater social support may moderate this association, thereby highlighting the potential importance of social support promoting interventions in mitigating the effect of ε4 × cumulative trauma burden on PTSD risk.

Further evidence for a role of the ADRB2 gene in risk for posttraumatic stress disorder

The aim of the present study was to attempt to replicate the recently reported finding associating rs2400707 of the Adrenoceptor Beta 2, Surface (ADRB2) gene and childhood trauma on PTSD symptoms. Participants included a predominantly veteran cohort of non-Hispanic blacks (NHB; n = 949) and a pre-dominantly veteran cohort of non-Hispanic whites (NHW; n = 759). No main effects were observed for rs2400707 on PTSD diagnosis. Among the NHB participants, we observed an interaction between rs2400707 and history of childhood trauma, whereby with each additional A allele, the odds of having PTSD increased by 1.31, but only among those who had experienced childhood trauma (p = 0.038). The interaction with rs2400707 and childhood trauma was not observed among the NHW study participants (p = 0.892). Taken together, the findings from the present research provide further evidence that the adrenergic system may be an important modulator of PTSD risk; however, additional work is still needed to clarify the exact nature of the relationship between PTSD and rs2400707 of the ADRB2 gene.

Development of a Melting Curve-Based Allele-Specific PCR of Apolipoprotein E (APOE) Genotyping Method for Genomic DNA, Guthrie Blood Spot, and Whole Blood

Genetic polymorphisms of apolipoprotein E (APOE) are associated with various health conditions and diseases, such as Alzheimer's disease, cardiovascular diseases, type 2 diabetes, etc. Hence, genotyping of APOE has broad applications in biomedical research and clinical settings, particularly in the era of precision medicine. The study aimed to develop a convenient and accurate method with flexible throughput to genotype the APOE polymorphisms. A melting curve-based allele-specific PCR method was developed to genotype two single nucleotide polymorphisms (SNPs) of APOE, i.e. rs429358 at codon 112 and rs7412 at codon 158. These two SNPs determine the genotype of APOE2, E3, and E4. PCR-based Sanger sequencing was used as the reference method for APOE genotyping. A 100% concordance rate was obtained in 300 subjects between the melting curve-based allele-specific PCR method and the Sanger sequencing method. This method was applied to a genetic association analysis of APOE and schizophrenia consisting of 711 patients with schizophrenia and 665 control subjects from Taiwan. However, no significant differences in the allele and genotype frequencies were detected between these two groups. Further experiments showed that DNA dissolved from blood collected on Guthrie filter paper and total blood cell lysate without DNA extraction can be used in the melting curve-based allele-specific PCR method. Thus, we suggest that this is a fast, accurate and robust APOE genotyping method with a flexible throughput and suitable for DNA template from different preparations. This convenient method shall meet the different needs of various research and clinical laboratories.

Plasma Lipidomic Profiling in a Military Population of Mild Traumatic Brain Injury and Post-Traumatic Stress Disorder with Apolipoprotein E ɛ4-Dependent Effect

In the military population, there is high comorbidity between mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) due to the inherent risk of psychological trauma associated with combat. These disorders present with long-term neurological dysfunction and remain difficult to diagnose due to their comorbidity and overlapping clinical presentation. Therefore, we performed cross-sectional analysis of blood samples from demographically matched soldiers (total, n = 120) with mTBI, PTSD, and mTBI+PTSD and those who were considered cognitively and psychologically normal. Soldiers were genotyped for apolipoprotein E (APOE) ɛ4, and phospholipids (PL) were examined using liquid chromatography/mass spectrometry analysis. We observed significantly lower levels of several major PL classes in TBI, PTSD, and TBI+PTSD, compared with controls. PTSD severity analysis revealed that significant PL decreases were primarily restricted to the moderate-to-severe PTSD group. An examination of the degree of unsaturation showed that monounsaturated fatty acid-containing phosphatidylcholine (PC) and phosphatidylinositol (PI) species were lower in the TBI and TBI+PTSD groups. However, these PLs were unaltered among PTSD subjects, compared with controls. Similarly, ether PC (ePC) levels were lower in PTSD and TBI+PTSD subjects, relative to controls. Ratios of arachidonic acid (AA) to docosahexaenoic acid (DHA)-containing species were significantly decreased within PC and phosphatidylethanolamine (PE) classes. APOE ɛ4 (+) subjects exhibited higher PL levels than their APOE ɛ4 (-) counterparts within the same diagnostic groups. These findings suggest that PL profiles, together with APOE genotyping, could potentially aid to differentiate diagnosis of mTBI and PTSD and warrant further validation. In conclusion, PL profiling may facilitate clinical diagnosis of mTBI and PTSD currently hindered by comorbid pathology and overlapping symptomology of these two conditions.

Brain-derived neurotropic factor polymorphisms, traumatic stress, mild traumatic brain injury, and combat exposure contribute to postdeployment traumatic stress

BACKGROUND

In addition to experiencing traumatic events while deployed in a combat environment, there are other factors that contribute to the development of posttraumatic stress disorder (PTSD) in military service members. This study explored the contribution of genetics, childhood environment, prior trauma, psychological, cognitive, and deployment factors to the development of traumatic stress following deployment.

METHODS

Both pre- and postdeployment data on 231 of 458 soldiers were analyzed. Postdeployment assessments occurred within 30 days from returning stateside and included a battery of psychological health, medical history, and demographic questionnaires; neurocognitive tests; and blood serum for the D2 dopamine receptor (DRD2), apolipoprotein E (APOE), and brain-derived neurotropic factor (BDNF) genes.

RESULTS

Soldiers who screened positive for traumatic stress at postdeployment had significantly higher scores in depression (d = 1.91), anxiety (d = 1.61), poor sleep quality (d = 0.92), postconcussion symptoms (d = 2.21), alcohol use (d = 0.63), traumatic life events (d = 0.42), and combat exposure (d = 0.91). BDNF Val66 Met genotype was significantly associated with risk for sustaining a mild traumatic brain injury (mTBI) and screening positive for traumatic stress. Predeployment traumatic stress, greater combat exposure and sustaining an mTBI while deployed, and the BDNF Met/Met genotype accounted for 22% of the variance of postdeployment PTSD scores (R (2)  = 0.22, P < 0.001). However, predeployment traumatic stress, alone, accounted for 17% of the postdeployment PTSD scores.

CONCLUSION

These findings suggest predeployment traumatic stress, genetic, and environmental factors have unique contributions to the development of combat-related traumatic stress in military service members.

Gene-Environment Interplay in Physical, Psychological, and Cognitive Domains in Mid to Late Adulthood: Is APOE a Variability Gene?

Despite emerging interest in gene-environment interaction (GxE) effects, there is a dearth of studies evaluating its potential relevance apart from specific hypothesized environments and biometrical variance trends. Using a monozygotic within-pair approach, we evaluated evidence of G×E for body mass index (BMI), depressive symptoms, and cognition (verbal, spatial, attention, working memory, perceptual speed) in twin studies from four countries. We also evaluated whether APOE is a 'variability gene' across these measures and whether it partly represents the 'G' in G×E effects. In all three domains, G×E effects were pervasive across country and gender, with small-to-moderate effects. Age-cohort trends were generally stable for BMI and depressive symptoms; however, they were variable-with both increasing and decreasing age-cohort trends-for different cognitive measures. Results also suggested that APOE may represent a 'variability gene' for depressive symptoms and spatial reasoning, but not for BMI or other cognitive measures. Hence, additional genes are salient beyond APOE.

Effect of genetic variation in the nicotinic receptor genes on risk for posttraumatic stress disorder

The present study examined the association between genetic variation in the nicotinic receptor gene family (CHRNA2, CHRNA3, CHRNA4, CHRNA5, CHRNA6, CHRNA7, CHRNA9, CHRNA10, CHRNB2, CHRNB3, CHRNB4) and the occurrence of posttraumatic stress disorder (PTSD). Clinical interviews were used to diagnose PTSD in 925 non-Hispanic Black (NHB) and 743 non-Hispanic White (NHW) participants. Trauma history and smoking status were assessed with self-report. No significant main effects or single nucleotide polymorphism (SNP) * smoking interactions were observed among NHB participants; however, among NHW participants, a novel association between rs12898919 in the cholinergic receptor nicotinic alpha-5 (CHRNA5) gene and PTSD was observed. No other significant main effects or SNP * smoking interactions were identified among NHW participants. While preliminary, these findings provide continued support for the hypothesis that the CHRNA5 gene is associated with increased risk for PTSD. Limitations of the present study include cross-sectional design, relatively small sample sizes for genetic research, use of self-report to assess smoking status, and use of different methods to diagnose PTSD. Additional research in other samples of trauma-exposed participants is needed to identify the specific functional variant(s) responsible for the association observed between CHRNA5 and PTSD risk in the present study.

Genome-wide association study of posttraumatic stress disorder in a cohort of Iraq-Afghanistan era veterans

BACKGROUND

Posttraumatic stress disorder (PTSD) is a psychiatric disorder that can develop after experiencing traumatic events. A genome-wide association study (GWAS) design was used to identify genetic risk factors for PTSD within a multi-racial sample primarily composed of U.S. veterans.

METHODS

Participants were recruited at multiple medical centers, and structured interviews were used to establish diagnoses. Genotypes were generated using three Illumina platforms and imputed with global reference data to create a common set of SNPs. SNPs that increased risk for PTSD were identified with logistic regression, while controlling for gender, trauma severity, and population substructure. Analyses were run separately in non-Hispanic black (NHB; n = 949) and non-Hispanic white (NHW; n = 759) participants. Meta-analysis was used to combine results from the two subsets.

RESULTS

SNPs within several interesting candidate genes were nominally significant. Within the NHB subset, the most significant genes were UNC13C and DSCAM. Within the NHW subset, the most significant genes were TBC1D2, SDC2 and PCDH7. In addition, PRKG1 and DDX60L were identified through meta-analysis. The top genes for the three analyses have been previously implicated in neurologic processes consistent with a role in PTSD. Pathway analysis of the top genes identified alternative splicing as the top GO term in all three analyses (FDR q < 3.5 × 10(-5)).

LIMITATIONS

No individual SNPs met genome-wide significance in the analyses.

CONCLUSIONS

This multi-racial PTSD GWAS identified biologically plausible candidate genes and suggests that post-transcriptional regulation may be important to the pathology of PTSD; however, replication of these findings is needed.

ApoE2 Exaggerates PTSD-Related Behavioral, Cognitive, and Neuroendocrine Alterations

Apolipoprotein E (apoE) is an essential component of lipoprotein particles in both the brain and periphery, and exists in three isoforms in the human population: E2, E3, and E4. ApoE has numerous, well-established roles in neurobiology. Most notably, E4 is associated with earlier onset and increased risk of Alzheimer's disease (AD). Although possession of E2 is protective in the context of AD, E2 appears to confer an increased incidence and severity of posttraumatic stress disorder (PTSD). However, the biological processes underlying this link remain unclear. In this study, we began to elucidate these associations by examining the effects of apoE on PTSD severity in combat veterans, and on PTSD-like behavior in mice with human apoE. In a group of 92 veterans with PTSD, we observed significantly higher Clinician-Administered PTSD Scale and PTSD Checklist scores in E2+ individuals, as well as alterations in salivary cortisol levels. Furthermore, we measured behavioral and biological outcomes in mice expressing human apoE after a single stressful event as well as following a period of chronic variable stress, a model of combat-related trauma. Mice with E2 showed impairments in fear extinction, and behavioral, cognitive, and neuroendocrine alterations following trauma. To the best of our knowledge, these data constitute the first translational demonstration of PTSD severity in men and PTSD-like symptoms in mice with E2, and point to apoE as a novel biomarker of susceptibility, and potential therapeutic target, for PTSD.

EFFECT OF THE APOE ε4 ALLELE AND COMBAT EXPOSURE ON PTSD AMONG IRAQ/AFGHANISTAN-ERA VETERANS

BACKGROUND

The apolipoprotein E (APOE) ε4 allele has been implicated in a range of neuropsychiatric conditions. The present research examined if the ε4 allele of the APOE gene moderated the effect of combat exposure on posttraumatic stress disorder (PTSD) among Iraq/Afghanistan-era veterans.

METHOD

Participants included 765 non-Hispanic White (NHW) and 859 non-Hispanic Black (NHB) Iraq/Afghanistan-era veterans. A structured interview established psychiatric diagnoses. Combat exposure and PTSD symptom severity were assessed via self-report.

RESULTS

The most common lifetime diagnoses were depression (39.2%), PTSD (38.4%), and alcohol dependence (24.38%). After correcting for multiple comparisons, no significant effects were observed on any of the outcomes among the NHW sample; however, within the NHB sample, significant gene × environment (G × E) interactions were observed for lifetime PTSD (P = .0029) and PTSD symptom severity (P = .0009). In each case, the APOE ε4 allele had no effect on the outcomes when combat exposure was low; however, when combat exposure was high, an additive effect was observed such that ε4 homozygotes exposed to high levels of combat reported the highest rates of PTSD (92%) and the worst symptom severity scores on the Davidson Trauma Scale (M = 79.5).

CONCLUSIONS

Although preliminary, these findings suggest that the APOE ε4 allele, in conjunction with exposure to high levels of combat exposure, may increase veterans' risk for developing PTSD.

An examination of the association between 5-HTTLPR, combat exposure, and PTSD diagnosis among U.S. veterans

Objective

To examine the association between the 5-HTTLPR polymorphism of the serotonin transporter (SLC6A4) gene, combat exposure, and posttraumatic stress disorder (PTSD) diagnosis and among two samples of combat-exposed veterans.

Method

The first sample included 550 non-Hispanic Black (NHB) combat-exposed veterans. The second sample included 555 non-Hispanic White (NHW) combat-exposed veterans. Participants were genotyped for the 5-HTTLPR/rs25531 variants of the SLC6A4 gene. A structured clinical interview was used to diagnose PTSD. Combat and civilian trauma exposure were assessed with validated self-report instruments. Logistic regression was used to test for main effects of 5-HTTLPR on PTSD diagnosis as well as gene x environment (GxE) interactions after adjusting for sex, ancestry proportion scores, civilian trauma exposure, and combat exposure.

Results

Within the NHB sample, a significant additive effect was observed for 5-HTTLPR (OR = 1.502, p = .0025), such that the odds of having a current diagnosis of PTSD increased by 1.502 for each additional S’ allele. No evidence for an association between 5-HTTLPR and PTSD was observed in the NHW sample. In addition, no evidence for combat x 5-HTTLPR effects were observed in either sample.

Conclusion

The present study suggests that there may be an association between 5-HTTLPR genotype and PTSD diagnosis among NHB veterans; however, no evidence for the hypothesized 5-HTTLPR x combat interaction was found.

Maladaptive autonomic regulation in PTSD accelerates physiological aging

A core manifestation of post-traumatic stress disorder (PTSD) is a disconnection between physiological state and psychological or behavioral processes necessary to adequately respond to environmental demands. Patients with PTSD experience abnormal oscillations in autonomic states supporting either fight and flight behaviors or withdrawal, immobilization, and dissociation without an intervening “calm” state that would provide opportunities for positive social interactions. This defensive autonomic disposition is adaptive in dangerous and life threatening situations, but in the context of every-day life may lead to significant psychosocial distress and deteriorating social relationships. The perpetuation of these maladaptive autonomic responses may contribute to the development of comorbid mental health issues such as depression, loneliness, and hostility that further modify the nature of cardiovascular behavior in the context of internal and external stressors. Over time, changes in autonomic, endocrine, and immune function contribute to deteriorating health, which is potently expressed in brain dysfunction and cardiovascular disease. In this theoretical review paper, we present an overview of the literature on the chronic health effects of PTSD. We discuss the brain networks underlying PTSD in the context of autonomic efferent and afferent contributions and how disruption of these networks leads to poor health outcomes. Finally, we discuss treatment approaches based on our theoretical model of PTSD.

Genomic predictors of combat stress vulnerability and resilience in U.S. Marines: A genome-wide association study across multiple ancestries implicates PRTFDC1 as a potential PTSD gene

BACKGROUND

Research on the etiology of post-traumatic stress disorder (PTSD) has rapidly matured, moving from candidate gene studies to interrogation of the entire human genome in genome-wide association studies (GWAS). Here we present the results of a GWAS performed on samples from combat-exposed U.S. Marines and Sailors from the Marine Resiliency Study (MRS) scheduled for deployment to Iraq and/or Afghanistan. The MRS is a large, prospective study with longitudinal follow-up designed to identify risk and resiliency factors for combat-induced stress-related symptoms. Previously implicated PTSD risk loci from the literature and polygenic risk scores across psychiatric disorders were also evaluated in the MRS cohort.

METHODS

Participants (N=3494) were assessed using the Clinician-Administered PTSD Scale and diagnosed using the DSM-IV diagnostic criterion. Subjects with partial and/or full PTSD diagnosis were called cases, all other subjects were designated controls, and study-wide maximum CAPS scores were used for longitudinal assessments. Genomic DNA was genotyped on the Illumina HumanOmniExpressExome array. Individual genetic ancestry was determined by supervised cluster analysis for subjects of European, African, Hispanic/Native American, and other descent. To test for association of SNPs with PTSD, logistic regressions were performed within each ancestry group and results were combined in meta-analyses. Measures of childhood and adult trauma were included to test for gene-by-environment (GxE) interactions. Polygenic risk scores from the Psychiatric Genomic Consortium were used for major depressive disorder (MDD), bipolar disorder (BPD), and schizophrenia (SCZ).

RESULTS

The array produced >800K directly genotyped and >21M imputed markers in 3494 unrelated, trauma-exposed males, of which 940 were diagnosed with partial or full PTSD. The GWAS meta-analysis identified the phosphoribosyl transferase domain containing 1 gene (PRTFDC1) as a genome-wide significant PTSD locus (rs6482463; OR=1.47, SE=0.06, p=2.04×10(-9)), with a similar effect across ancestry groups. Association of PRTFDC1 with PTSD in an independent military cohort showed some evidence for replication. Loci with suggestive evidence of association (n=25 genes, p<5×10(-6)) further implicated genes related to immune response and the ubiquitin system, but these findings remain to be replicated in larger GWASs. A replication analysis of 25 putative PTSD genes from the literature found nominally significant SNPs for the majority of these genes, but associations did not remain significant after correction for multiple comparison. A cross-disorder analysis of polygenic risk scores from GWASs of BPD, MDD, and SCZ found that PTSD diagnosis was associated with risk sores of BPD, but not with MDD or SCZ.

CONCLUSIONS

This first multi-ethnic/racial GWAS of PTSD highlights the potential to increase power through meta-analyses across ancestry groups. We found evidence for PRTFDC1 as a potential novel PTSD gene, a finding that awaits further replication. Our findings indicate that the genetic architecture of PTSD may be determined by many SNPs with small effects, and overlap with other neuropsychiatric disorders, consistent with current findings from large GWAS of other psychiatric disorders.

Post-traumatic stress symptoms and adult attachment: a 24-year longitudinal study

OBJECTIVES

Attachment theory has become a key framework for understanding responses to and consequences of trauma across the life course. We predicted that more severe post-traumatic stress (PTS) symptoms at age 37 years would be associated with insecure attachment at age 55 and with worse PTS symptoms 24 years later at age 61, and that age 55 attachment would mediate the influence of earlier PTS symptoms on later symptoms.

DESIGN

Data on PTS self-reported symptoms were available for 975 community-dwelling participants from the longitudinal Vietnam Era Twin Study of Aging at ages 37 and 61 years. At age 55, participants completed the Experiences in Close Relationships Inventory, a measure of adult attachment.

RESULTS

PTS symptoms at ages 37 and 61 correlated (r = 0.43; p <0.0001). Multiple mediation models found significant direct effects of age 37 PTS symptoms on age 61 PTS symptoms (β = 0.26; 95% confidence interval: 0.19-0.33). Anxious and avoidant attachment at age 55 predicted PTS symptoms at age 61 (r = 0.34 and 0.25; ps <0.0001, respectively) and also significantly mediated PTS symptoms over time, showing that insecure attachment increased PTS severity. Participants with higher age 37 PTS symptoms were more likely to have a history of divorce; marital status did not mediate PTS.

CONCLUSIONS

Analyses demonstrate the persistence of PTS symptoms from early midlife into early old age. Mediation analyses revealed that one path through which PTS symptoms persisted was indirect: through their influence on attachment insecurity. This study provides insight into ongoing interconnections between psychological and interpersonal responses to stress.

Progress towards understanding the genetics of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a complex syndrome that occurs following exposure to a potentially life threatening traumatic event. This review summarises the literature on the genetics of PTSD including gene-environment interactions (GxE), epigenetics and genetics of treatment response. Numerous genes have been shown to be associated with PTSD using candidate gene approaches. Genome-wide association studies have been limited due to the large sample size required to reach statistical power. Studies have shown that GxE interactions are important for PTSD susceptibility. Epigenetics plays an important role in PTSD susceptibility and some of the most promising studies show stress and child abuse trigger epigenetic changes. Much of the molecular genetics of PTSD remains to be elucidated. However, it is clear that identifying genetic markers and environmental triggers has the potential to advance early PTSD diagnosis and therapeutic interventions and ultimately ease the personal and financial burden of this debilitating disorder.

Interaction of APOE genotype and testosterone on episodic memory in middle-aged men

Age-related changes in testosterone are believed to be a key component of the processes that contribute to cognitive aging in men. The APOE-ε4 allele may interact with testosterone and moderate the hormone's association with cognition. The goals of the present study were to examine the degree to which free testosterone is associated with episodic memory in a community-based sample of middle-aged men, and examine the potential interaction between free testosterone and the APOE-ε4 allele. Data were used from 717 participants in the Vietnam Era Twin Study of Aging. Average age was 55.4 years (standard deviation = 2.5). Significant positive associations were observed between free testosterone level and verbal episodic memory, as well as a significant interaction between free testosterone and APOE-ε4 status. In ε4 carriers free testosterone was positively associated with verbal episodic memory performance (story recall), whereas no association was observed in ε4 noncarriers. Results support the hypothesis that APOE-ε4 status increases susceptibility to other risk factors, such as low testosterone, which may ultimately contribute to cognitive decline or dementia.