Depressive symptoms are not associated with leukocyte telomere length: findings from the Nova Scotia Health Survey (NSHS95), a population-based study

Causal relationship between depression and aging: a bidirectional two-sample Mendelian randomization study

BACKGROUND

The causal relationship and the direction of the effect between depression and aging remain controversial.

METHODS

We used a bidirectional two-sample Mendelian randomization analysis to examine the relationship between depression and age proxy indicators. We obtained pooled statistics from genome-wide association studies (GWAS) on depression and the age proxy indicators. We employed five MR analysis methods to address potential biases and ensure robustness of our results, with the inverse variance weighted (IVW) method being the primary outcome. We also conducted outlier exclusion using Radial MR, MRPRESSO, and MR Steiger filters. Additionally, sensitivity analyses were performed to assess heterogeneity and pleiotropy.

RESULTS

Our MR analysis revealed that depression causally leads to shortened telomere length (β = - 0.014; P = 0.038), increased frailty index (β = 0.076; P = 0.000), and accelerated GrimAge (β = 0.249; P = 0.024). Furthermore, our findings showed that the frailty index (OR = 1.679; P = 0.001) was causally associated with an increased risk of depression. Additionally, we found that appendicular lean mass (OR = 0.929; P = 0.000) and left-hand grip strength (OR = 0.836; P = 0.014) were causally associated with a reduced risk of depression. Sensitivity analyses demonstrated the robustness of our findings.

CONCLUSIONS

Our study provides evidence that depression contributes to the accelerated aging process, resulting in decreased telomere length, increased frailty index, and accelerated GrimAge. Additionally, we found that the frailty index increases the risk of depression, while appendicular lean mass and left-handed grip strength reduce the risk of depression.

Childhood adversities are associated with shorter leukocyte telomere length at adult age in a population-based study

Telomeres are repeat sequences and an associated protein complex located at the end of the chromosomes. They shorten with every cell division and are regarded markers for cellular aging. Shorter leukocyte telomere length (LTL) has been observed in many complex diseases, including psychiatric disorders. However, analyses focusing on psychiatric disorders are mainly based on clinical samples and the significance of shorter LTL on the population level remains uncertain. We addressed this question in a population-based sample from Finland (N = 7142). The survey was performed and the blood samples were collected in 2000-2001 to assess major public health problems and their determinants. DSM-IV diagnoses of major psychiatric illnesses were obtained by interview using the Composite International Diagnostic Interview. Information regarding their risk factors, including the number of self-reported childhood adversities, recent psychological distress, and sleep difficulties was collected by questionnaires. LTL was measured by qPCR. None of the studied psychiatric illnesses, sleep difficulties, or recent psychological distress associated with LTL. However, individuals with three or more childhood adversities had shorter LTL at adult age (β = -0.006, P = 0.005). Also, current occupational status was associated with LTL (β = -0.03, P = 0.04). These effects remained significant after adjusting for known LTL-associated lifestyle or sociodemographic factors. In conclusion, relatively common childhood adversities were associated with shorter LTL at adult age in a nationally representative population-based cohort, implying that childhood adversities may cause accelerated telomere shortening. Our finding has potentially important implications as it supports the view that childhood adversities have an impact on psychological and somatic well-being later in life.

Telomere Shortening and Psychiatric Disorders: A Systematic Review

Telomeres are aging biomarkers, as they shorten while cells undergo mitosis. The aim of this study was to evaluate whether psychiatric disorders marked by psychological distress lead to alterations to telomere length (TL), corroborating the hypothesis that mental disorders might have a deeper impact on our physiology and aging than it was previously thought. A systematic search of the literature using MeSH descriptors of psychological distress ("Traumatic Stress Disorder" or "Anxiety Disorder" or "depression") and telomere length ("cellular senescence", "oxidative stress" and "telomere") was conducted on PubMed, Cochrane Library and ScienceDirect databases. A total of 56 studies (113,699 patients) measured the TL from individuals diagnosed with anxiety, depression and posttraumatic disorders and compared them with those from healthy subjects. Overall, TL negatively associates with distress-related mental disorders. The possible underlying molecular mechanisms that underly psychiatric diseases to telomere shortening include oxidative stress, inflammation and mitochondrial dysfunction linking. It is still unclear whether psychological distress is either a cause or a consequence of telomere shortening.

An update in toxicology of ageing

The field of ageing research has been rapidly advancing in recent decades and it had provided insight into the complexity of ageing phenomenon. However, as the organism-environment interaction appears to significantly affect the organismal pace of ageing, the systematic approach for gerontogenic risk assessment of environmental factors has yet to be established. This puts demand on development of effective biomarker of ageing, as a relevant tool to quantify effects of gerontogenic exposures, contingent on multidisciplinary research approach. Here we review the current knowledge regarding the main endogenous gerontogenic pathways involved in acceleration of ageing through environmental exposures. These include inflammatory and oxidative stress-triggered processes, dysregulation of maintenance of cellular anabolism and catabolism and loss of protein homeostasis. The most effective biomarkers showing specificity and relevancy to ageing phenotypes are summarized, as well. The crucial part of this review was dedicated to the comprehensive overview of environmental gerontogens including various types of radiation, certain types of pesticides, heavy metals, drugs and addictive substances, unhealthy dietary patterns, and sedentary life as well as psychosocial stress. The reported effects in vitro and in vivo of both recognized and potential gerontogens are described with respect to the up-to-date knowledge in geroscience. Finally, hormetic and ageing decelerating effects of environmental factors are briefly discussed, as well.

Telomere Length and ADHD Symptoms in Young Adults

Objective: Previous research examining telomeres in individuals with neuropsychiatric disorders shows that greater illness, symptoms, or cognitive impairment are linked with shorter telomeres. However, the relationships of telomere length and neuropsychological processes or psychiatric symptoms are not understood in individuals with Attention Deficit/Hyperactivity Disorder (ADHD). Method: 390 young adults with and without ADHD completed a multi-informant diagnostic assessment and neuropsychological testing battery. Participant DNA was isolated from saliva samples, and telomere length was determined using qPCR. Results: Linear regression models demonstrated the only significant association to survive correction for multiple testing was for childhood hyperactivity-impulsivity symptoms and longer telomere length. Conclusion: Contrary to expectations, longer telomere length in young adults was associated only with childhood ADHD symptoms, particularly hyperactivity-impulsivity, in this sample. These findings are an important demonstration that the neuropsychological deficits and symptoms experienced by individuals diagnosed with ADHD during adulthood may not be negatively associated with telomere length.

Leukocyte Telomere Length Is Unrelated to Cognitive Performance Among Non-Demented and Demented Persons: An Examination of Long Life Family Study Participants

OBJECTIVE

Leukocyte telomere length (LTL) is a widely hypothesized biomarker of biological aging. Persons with shorter LTL may have a greater likelihood of developing dementia. We investigate whether LTL is associated with cognitive function, differently for individuals without cognitive impairment versus individuals with dementia or incipient dementia.

METHOD

Enrolled subjects belong to the Long Life Family Study (LLFS), a multi-generational cohort study, where enrollment was predicated upon exceptional family longevity. Included subjects had valid cognitive and telomere data at baseline. Exclusion criteria were age ≤ 60 years, outlying LTL, and missing sociodemographic/clinical information. Analyses were performed using linear regression with generalized estimating equations, adjusting for sex, age, education, country, generation, and lymphocyte percentage.

RESULTS

Older age and male gender were associated with shorter LTL, and LTL was significantly longer in family members than spouse controls (p < 0.005). LTL was not associated with working or episodic memory, semantic processing, and information processing speed for 1613 cognitively unimpaired individuals as well as 597 individuals with dementia or incipient dementia (p < 0.005), who scored significantly lower on all cognitive domains (p < 0.005).

CONCLUSIONS

Within this unique LLFS cohort, a group of families assembled on the basis of exceptional survival, LTL is unrelated to cognitive ability for individuals with and without cognitive impairment. LTL does not change in the context of degenerative disease for these individuals who are biologically younger than the general population.

The relation of telomere length at midlife to subsequent 20-year depression trajectories among women

BACKGROUND

Telomeres cap and protect DNA but shorten with each somatic cell division. Aging and environmental and lifestyle factors contribute to the speed of telomere attrition. Current evidence suggests a link between relative telomere length (RTL) and depression but the directionality of the relationship remains unclear. We prospectively examined associations between RTL and subsequent depressive symptom trajectories.

METHODS

Among 8,801 women of the Nurses' Health Study, depressive symptoms were measured every 4 years from 1992 to 2012; group-based trajectories of symptoms were identified using latent class growth-curve analysis. Multinomial logistic models were used to relate midlife RTLs to the probabilities of assignment to subsequent depressive symptom trajectory groups.

RESULTS

We identified four depressive symptom trajectory groups: minimal depressive symptoms (62%), worsening depressive symptoms (14%), improving depressive symptoms (19%), and persistent-severe depressive symptoms (5%). Longer midlife RTLs were related to significantly lower odds of being in the worsening symptoms trajectory versus minimal trajectory but not to other trajectories. In comparison with being in the minimal symptoms group, the multivariable-adjusted odds ratio of being in the worsening depressive symptoms group was 0.78 (95% confidence interval, 0.62-0.97; p = 0.02), for every standard deviation increase in baseline RTL.

CONCLUSIONS

In this large prospective study of generally healthy women, longer telomeres at midlife were associated with significantly lower risk of a subsequent trajectory of worsening mood symptoms over 20 years. The results raise the possibility of telomere shortening as a novel contributing factor to late-life depression.

Effects of Inflammation and Depression on Telomere Length in Young Adults in the United States

Little is known about the associations of inflammation and depression with telomere length. Using data from the National Health and Nutrition Examination Survey (NHANES) 1999–2002, the current study assessed the effects of inflammation and depression on telomere length in 1141 young adults in the USA. Depression status was assessed from the World Health Organization Composite International Diagnostic Interview and inflammation status was measured based on C-reactive protein (CRP) concentrations. Information on telomere length was obtained using the quantitative polymerase chain reaction method to measure telomere length relative to standard reference DNA (T/S ratio). Unadjusted and adjusted linear and logistic regression models were used to assess the relationship between the tertiles of CRP concentration and the telomere length stratified by the status of depression such as major depression or depressed affect vs. no depression. The adjusted models were controlled for age, family poverty income ratio, race/ethnicity, marital status, physical activity, body mass index, and alcohol drinking status. A significant and decreasing linear trend in telomere length was found as CRP levels increased in men, regardless of the depression status, and women with major depression or depressed affect (p values < 0.05). Among men without depression, those with an elevated CRP level had increased odds of having a shortened telomere length compared to men with low CRP levels after controlling for covariates (adjusted odds ratio 1.77, 95% confidence interval (CI) 1.09–2.90). In women, there was no association between CRP and telomere length, regardless of the depression status. In conclusion, there was a significant and inverse association between inflammation and telomere length according to the depression status in men but not in women. The present findings may be of clinical significance for the monitoring of inflammation levels and depression status as determinants of telomere length.

Association between telomere length and completed suicide observed in 71 suicide victims - Preliminary findings

OBJECTIVE

Telomere length has emerged as a cumulative marker for lifestyle, psychosocial stress, and cytotoxic environments. We aimed to examine the possible association between leukocyte telomere length (LTL) and completed suicide.

METHODS

This study included 71 suicide completers and 117 healthy controls for whom LTL was determined by the ratio of the telomere repeat copy number to the single-copy gene copy number (T/S ratio). We compared the LTL between the suicide completers and the healthy controls and estimated the odds ratio (OR) for suicide for each age group, applying a generalized estimating equation (GEE).

RESULTS

LTL was significantly shortened in the suicide completers as compared with the controls, overall subjects, or within-age categories (≤29 and 30-49 years). Furthermore, a longer LTL was associated with significantly decreased odds of completed suicide for those aged ≤29 years and 30-49 years (OR = 0.11, 95% confidence interval [CI] 0.03-0.37, p < .001 for the ≤29-year age group; OR = 0.54, 95% CI 0.34-0.84, p = .006 for the 30- to 49-year age group).

CONCLUSIONS

This study provides evidence regarding the relationship between shortened LTL and completed suicide, especially in those aged <50 years. Future research should further assess potential confounders and examine underlying mechanisms.

Telomeres in neurological disorders

Ever since their discovery, the telomeres and the telomerase have been topics of intensive research, first as a mechanism of cellular aging and later as an indicator of health and diseases in humans. By protecting the chromosome ends, the telomeres play a vital role in preserving the information in our genome. Telomeres shorten with age and the rate of telomere erosion provides insight into the proliferation history of cells. The pace of telomere attrition is known to increase at the onset of several pathological conditions. Telomere shortening has been emerging as a potential contributor in the pathogenesis of several neurological disorders including autism spectrum disorders (ASD), schizophrenia, Alzheimer's disease (AD), Parkinson's disease (PD) and depression. The rate of telomere attrition in the brain is slower than that of other tissues owing to the low rate of cell proliferation in brain. Telomere maintenance is crucial for the functioning of stem cells in brain. Taking together the studies on telomere attrition in various neurological disorders, an association between telomere shortening and disease status has been demonstrated in schizophrenia, AD and depression, in spite of a few negative reports. But, studies in ASD and PD have failed to produce conclusive results. The cause-effect relationship between TL and neurological disorders is yet to be elucidated. The factors responsible for telomere erosion, which have also been implicated in the pathogenesis of neurological disorders, need to be explored in detail. Telomerase activation is now being considered as a potential therapeutic strategy for neurological disorders.

Spousal concordance in telomere length: New evidence from older adults in the US

Telomere length (TL) has been associated with a range of aging outcomes as well as mortality. Recent research has shown both high heritability (~70%) of TL as well as moderate spousal similarity (r~0.3) using European datasets. This paper explores the level of spousal concordance in telomere length in the Health and Retirement Study, a national sample of adults in the US. The results show that the spousal correlations are lower (r~0.11). Regression-based associations in TL in the US are low (beta~0.08) and also vary by the number of times respondents have been married, where spouses married a single time have higher associations in TL (beta~.12) than spouses married more once (beta~0.03). I also find variation in spousal TL association levels based on husband’s education level. These findings suggest the possibility of both assortative mating patterns related to telomere length as well as likelihood of shared environmental factors that cause TL similarity in people who are socially connected.

Telomere length and depression: prospective cohort study and Mendelian randomisation study in 67 306 individuals

BACKGROUND

Depression has been cross-sectionally associated with short telomeres as a measure of biological age. However, the direction and nature of the association is currently unclear.

AIMS

We examined whether short telomere length is associated with depression cross-sectionally as well as prospectively and genetically.

METHOD

Telomere length and three polymorphisms, TERT, TERC and OBFC1, were measured in 67 306 individuals aged 20-100 years from the Danish general population and associated with register-based attendance at hospital for depression and purchase of antidepressant medication.

RESULTS

Attendance at hospital for depression was associated with short telomere length cross-sectionally, but not prospectively. Further, purchase of antidepressant medication was not associated with short telomere length cross-sectionally or prospectively. Mean follow-up was 7.6 years (range 0.0-21.5). The genetic analyses suggested that telomere length was not causally associated with attendance at hospital for depression or with purchase of antidepressant medication.

CONCLUSIONS

Short telomeres were not associated with depression in prospective or in causal, genetic analyses.

Abnormal Bone Acquisition With Early-Life HIV Infection: Role of Immune Activation and Senescent Osteogenic Precursors

Chronic immune activation associated with human immunodeficiency virus (HIV) infection may have negative consequences on bone acquisition in individuals infected with HIV early in life. Bone mineral density (BMD) and microarchitecture were characterized in 38 HIV-infected men on antiretroviral therapy (18 perinatally-infected, 20 adolescence-infected) and 20 uninfected men age 20 to 25 years by dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HRpQCT). Flow cytometry was utilized to measure CD4+/CD8+ activation (HLADR+CD38+) and senescence (CD28-CD57+) and to quantify circulating osteogenic precursor (COP) cells in peripheral blood mononuclear cells using antibodies to RUNX2 and osteocalcin (OCN). Telomere lengths were measured in sorted COP cells using qPCR. DXA-derived areal BMD Z-scores and HRpQCT-derived volumetric BMD (vBMD) measures were lower in HIV-infected than uninfected men. Proportion of activated and senescent CD4+ and CD8+ T cells were higher in HIV-infected than uninfected men. The percentage of COP cells (mean ± SE) was lower in HIV-infected than uninfected (0.19% ± 0.02% versus 0.43% ± 0.06%; p < 0.0001) men, and also lower in perinatally-infected than adolescence-infected men (0.15% ± 0.02% versus 0.22% ± 0.03%; p < 0.04). A higher proportion of COP cells correlated with higher bone stiffness, a measure of bone strength, whereas a higher proportion of activated CD4+ T cells correlated with lower BMD and stiffness and lower proportion of COP cells. T cell activation with HIV-infection was associated with decreased numbers of osteogenic precursors as well as lower peak bone mass and bone strength. © 2016 American Society for Bone and Mineral Research.

Psychological Profiles in the Prediction of Leukocyte Telomere Length in Healthy Individuals

BACKGROUND

Shorter telomere length (TL) may signal premature cellular aging and increased risk for disease. While depression and psychosocial stress have been associated with shorter telomeres, other psychological risk factors for cardiovascular disease have received less attention.

PURPOSE

To evaluate the association between TL and psychological risk factors (symptoms of anxiety and depression, hostility and defensiveness traits) for heart disease, and to examine whether chronological age and sex moderate the associations observed.

METHODS

132 healthy men and women (Mage = 45.34 years) completed the Marlowe-Crowne Social Desirability Scale, the Beck Depression Inventory II, The Beck Anxiety Inventory and the Cook-Medley Hostility Scale. Relative TL was measured by quantitative polymerase chain reaction (PCR) of total genomic DNA samples. A series of hierarchical linear regressions were performed controlling for pertinent covariates.

RESULTS

Shorter TL was observed among individuals high in defensiveness (β = -.221) and depressive symptoms (β = -.213), as well as in those with less hostility (β =.256) and anxiety (β =.220)(all Ps<.05). Psychological variables explained 19% of the variance over and above that explained by covariates (age, sex, exercise, alcohol consumption, systemic inflammation, and 24-hr mean arterial pressure). Age moderated the relation between TL and defensiveness (β =.179, p =.03). Sex did not influence any of the relations.

CONCLUSIONS

Telomere length is associated with psychological burden though the direction of effect differs depending on the psychological variables under study. Further research is needed to determine the reasons for and implications of these seemingly contradictory findings.

Depression and telomere length: A meta-analysis

BACKGROUND

Several recent studies have investigated the relationship between telomere length and depression with inconsistent results. This meta-analysis examined whether telomere length and depression are associated and explored factors that might affect this association.

METHODS

Studies measuring telomere length in subjects with clinically significant unipolar depression were included. A comprehensive search strategy identified studies in PubMed, MEDLINE, PsycINFO, Global Health, The Cochrane Library, and Web of Science. A structured data abstraction form was used and studies were appraised for inclusion or exclusion using a priori conditions. Analyses were conducted using standardized mean differences in a continuous random effects model.

RESULTS

Thirty-eight studies (N=34,347) met the inclusion criteria. The association between depression and telomere length was significant, with a Cohen's d effect size of -0.205 (p<0.0001, I(2)=42%). Depression severity significantly associated with telomere length (p=0.03). Trim and fill analysis indicated the presence of publication bias (p=0.003), but that the association remained highly significant after accounting for the bias. Subgroup analysis revealed depression assessment tools, telomere measurement techniques, source tissue and comorbid medical conditions significantly affected the relationship.

LIMITATIONS

Other potentially important sub-groups, including antidepressant use, have not been investigated in sufficient detail or number yet and thus were not addressed in this meta-analysis.

CONCLUSIONS

There is a negative association between depression and telomere length. Further studies are needed to clarify potential causality underlying this association and to elucidate the biology linking depression and this cellular marker of stress exposure and aging.

Alterations of Mitochondrial DNA Copy Number and Telomere Length With Early Adversity and Psychopathology

BACKGROUND

Telomere shortening and alterations of mitochondrial biogenesis are involved in cellular aging. Childhood adversity is associated with telomere shortening, and several investigations have shown short telomeres in psychiatric disorders. Recent studies have examined whether mitochondria might be involved in neuropsychiatric conditions; findings are limited and no prior work has examined this in relation to stress exposure.

METHODS

Two-hundred ninety healthy adults provided information on childhood parental loss and maltreatment and completed diagnostic interviews. Participants were categorized into four groups based upon the presence or absence of childhood adversity and the presence or absence of lifetime psychopathology (depressive, anxiety, and substance use disorders). Telomere length and mitochondrial DNA (mtDNA) copy number were measured from leukocyte DNA by quantitative polymerase chain reaction.

RESULTS

Childhood adversity and lifetime psychopathology were each associated with shorter telomeres (p < .01) and higher mtDNA copy numbers (p < .001). Significantly higher mtDNA copy numbers and shorter telomeres were seen in individuals with major depression, depressive disorders, and anxiety disorders, as well as those with parental loss and childhood maltreatment. A history of substance disorders was also associated with significantly higher mtDNA copy numbers.

CONCLUSIONS

This study provides the first evidence of an alteration of mitochondrial biogenesis with early life stress and with anxiety and substance use disorders. We replicate prior work on telomere length and psychopathology and show that this effect is not secondary to medication use or comorbid medical illness. Finally, we show that early life stress and psychopathology are each associated with these markers of cellular aging.

Discrimination, mental health, and leukocyte telomere length among African American men

African American men in the US experience disparities across multiple health outcomes. A common mechanism underlying premature declines in health may be accelerated biological aging, as reflected by leukocyte telomere length (LTL). Racial discrimination, a qualitatively unique source of social stress reported by African American men, in tandem with poor mental health, may negatively impact LTL in this population. The current study examined cross-sectional associations between LTL, self-reported racial discrimination, and symptoms of depression and anxiety among 92 African American men 30-50 years of age. LTL was measured in kilobase pairs using quantitative polymerase chain reaction assay. Controlling for sociodemographic factors, greater anxiety symptoms were associated with shorter LTL (b=-0.029, standard error [SE]=0.014; p<0.05). There were no main effects of racial discrimination or depressive symptoms on LTL, but we found evidence for a significant interaction between the two (b=0.011, SE=0.005; p<0.05). Racial discrimination was associated with shorter LTL among those with lower levels of depressive symptoms. Findings from this study highlight the role of social stressors and individual-level psychological factors for physiologic deterioration among African American men. Consistent with research on other populations, greater anxiety may reflect elevated stress associated with shorter LTL. Racial discrimination may represent an additional source of social stress among African American men that has detrimental consequences for cellular aging among those with lower levels of depression.

Peripheral telomere length and hippocampal volume in adolescents with major depressive disorder

Several studies have reported that adults with major depressive disorder have shorter telomere length and reduced hippocampal volumes. Moreover, studies of adult populations without major depressive disorder suggest a relationship between peripheral telomere length and hippocampal volume. However, the relationship of these findings in adolescents with major depressive disorder has yet to be explored. We examined whether adolescent major depressive disorder is associated with altered peripheral telomere length and hippocampal volume, and whether these measures relate to one another. In 54 unmedicated adolescents (13-18 years) with major depressive disorder and 63 well-matched healthy controls, telomere length was assessed from saliva using quantitative polymerase chain reaction methods, and bilateral hippocampal volumes were measured with magnetic resonance imaging. After adjusting for age and sex (and total brain volume in the hippocampal analysis), adolescents with major depressive disorder exhibited significantly shorter telomere length and significantly smaller right, but not left hippocampal volume. When corrected for age, sex, diagnostic group and total brain volume, telomere length was not significantly associated with left or right hippocampal volume, suggesting that these cellular and neural processes may be mechanistically distinct during adolescence. Our findings suggest that shortening of telomere length and reduction of hippocampal volume are already present in early-onset major depressive disorder and thus unlikely to be only a result of accumulated years of exposure to major depressive disorder.

Genetic determinants of telomere length and risk of common cancers: a Mendelian randomization study

Epidemiological studies have reported inconsistent associations between telomere length (TL) and risk for various cancers. These inconsistencies are likely attributable, in part, to biases that arise due to post-diagnostic and post-treatment TL measurement. To avoid such biases, we used a Mendelian randomization approach and estimated associations between nine TL-associated SNPs and risk for five common cancer types (breast, lung, colorectal, ovarian and prostate cancer, including subtypes) using data on 51 725 cases and 62 035 controls. We then used an inverse-variance weighted average of the SNP-specific associations to estimate the association between a genetic score representing long TL and cancer risk. The long TL genetic score was significantly associated with increased risk of lung adenocarcinoma (P = 6.3 × 10(-15)), even after exclusion of a SNP residing in a known lung cancer susceptibility region (TERT-CLPTM1L) P = 6.6 × 10(-6)). Under Mendelian randomization assumptions, the association estimate [odds ratio (OR) = 2.78] is interpreted as the OR for lung adenocarcinoma corresponding to a 1000 bp increase in TL. The weighted TL SNP score was not associated with other cancer types or subtypes. Our finding that genetic determinants of long TL increase lung adenocarcinoma risk avoids issues with reverse causality and residual confounding that arise in observational studies of TL and disease risk. Under Mendelian randomization assumptions, our finding suggests that longer TL increases lung adenocarcinoma risk. However, caution regarding this causal interpretation is warranted in light of the potential issue of pleiotropy, and a more general interpretation is that SNPs influencing telomere biology are also implicated in lung adenocarcinoma risk.

Associations between the five-factor model of personality and leukocyte telomere length in elderly men and women: The Helsinki Birth Cohort Study (HBCS)

OBJECTIVE

Personality traits have been associated with cardiometabolic diseases and mental disorders as well as with longevity. However, the underlying mechanisms are not fully understood. Accelerated cellular aging may play a role in this process. We studied whether personality traits in late adulthood, as defined in the five-factor model (FFM), were associated with a biomarker of cellular vitality, leukocyte telomere length (LTL).

METHODS

At a mean age of 63.4 (SD=2.8) years, 1671 (742 men, 929 women) participants from the Helsinki Birth Cohort Study filled in the Neuroticism, Extraversion and Openness Personality Inventory (NEO-PI). LTL was measured at a mean age of 61.5 (SD=2.9) years by using a real-time quantitative PCR method.

RESULTS

None of the FFM personality dimensions were significantly associated with the LTL in the analyses of both sexes combined. We however found interaction between sex and agreeableness (B=0.020, 95% CI=.008, 0.032, p=.001) and in the sex-specific analyses, men who scored higher on agreeableness (B=-0.086, 95% CI=-0.155, -0.016, p=.016) and women who scored lower on agreeableness (B=0.074, 95% CI=0.014, 0.134, p=.016) had shorter LTL.

CONCLUSIONS

FFM dimensions of personality were not associated with LTL in a sample of elderly individuals. The counterintuitive and sporadic sex specific finding on agreeableness requires replication. Overall our findings suggest that LTL, a biomarker of cellular aging, may not offer insight into the associations between personality, longevity and health.

Telomere length and telomerase in a well-characterized sample of individuals with major depressive disorder compared to controls

BACKGROUND

Leukocyte telomere length (LTL) is a marker of cellular turnover and oxidative stress. Studies suggest major depressive disorder (MDD) is associated with oxidative stress, but examinations of MDD and LTL have yielded mixed results, likely because of differences in measurement methods and unmeasured confounding. This study examined LTL and telomerase activity in 166 individuals with MDD compared to 166 age- and gender-matched matched controls free of any psychiatric disorder, using well-validated assays and clinical assessment methods, and controlling for a range of potential confounders.

METHODS

Subjects aged 18 to 70 were evaluated by trained raters and provided blood for LTL and telomerase activity measurement. LTL was assayed using Southern blot and replicated with qPCR, and telomerase activity was assayed with a repeat amplification protocol using a commercial kit.

RESULTS

There was no significant difference in telomere length for individuals with MDD [mean (SD)=9.1 (3.0)kbp] compared to controls [mean(SD)=8.9(2.5)kbp] measured by Southern blot (p=0.65) or by confirmatory qPCR (p=0.91) assays. Controlling for potential confounders did not alter the results. Telomerase activity did not differ by MDD diagnosis overall (p=0.40), but the effect of MDD was significantly modified by gender (t(299)=2.67, p=0.0079) even after controlling for potential confounders, with telomerase activity significantly greater only in males with MDD versus controls.

CONCLUSION

Our well-characterized, well-powered examination of concurrently assessed telomere length and telomerase activity in individuals with clinically significant, chronic MDD and matched controls failed to provide strong evidence of an association of MDD with shorter LTL, while telomerase activity was higher in men with MDD [corrected].

Psychiatric disorders and leukocyte telomere length: Underlying mechanisms linking mental illness with cellular aging

Many psychiatric illnesses are associated with early mortality and with an increased risk of developing physical diseases that are more typically seen in the elderly. Moreover, certain psychiatric illnesses may be associated with accelerated cellular aging, evidenced by shortened leukocyte telomere length (LTL), which could underlie this association. Shortened LTL reflects a cell's mitotic history and cumulative exposure to inflammation and oxidation as well as the availability of telomerase, a telomere-lengthening enzyme. Critically short telomeres can cause cells to undergo senescence, apoptosis or genomic instability, and shorter LTL correlates with poorer health and predicts mortality. Emerging data suggest that LTL may be reduced in certain psychiatric illnesses, perhaps in proportion to exposure to the psychiatric illnesses, although conflicting data exist. Telomerase has been less well characterized in psychiatric illnesses, but a role in depression and in antidepressant and neurotrophic effects has been suggested by preclinical and clinical studies. In this article, studies on LTL and telomerase activity in psychiatric illnesses are critically reviewed, potential mediators are discussed, and future directions are suggested. A deeper understanding of cellular aging in psychiatric illnesses could lead to re-conceptualizing them as systemic illnesses with manifestations inside and outside the brain and could identify new treatment targets.

Telomere length is highly inherited and associated with hyperactivity-impulsivity in children with attention deficit/hyperactivity disorder

Telomere length (TL) is highly heritable, and a shorter telomere at birth may increase the risk of age-related problems. Additionally, a shorter TL may represent a biomarker of chronic stress and has been associated with psychiatric disorders. However, no study has explored whether there is an association between TL and the symptoms of one of the most common neurodevelopmental disorders in childhood: Attention Deficit/Hyperactive Disorder (ADHD). We evaluated 61 (range, 6–16 years) ADHD children and their parents between 2012 and 2014. TL was measured with a quantitative polymerase chain reaction method with telomere signal normalized to the signal from a single copy gene (36B4) to generate a T/S ratio. Family data was processed through a generalized estimated equations (GEE) model to determine the effect of parental TL on children TL. Inattentive and hyperactive-impulsive symptoms were also evaluated in relation to TL. For the first time, we found general heritability to be the major mechanism explaining interindividual TL variation in ADHD (father-child: 95% CI = 0.35/0.91, p < 0.001; mother-child: 95% CI = 0.38/0.74, p < 0.001). The hyperactive-impulsive dimension of ADHD was related with children’s TL (r = −339, p = 0.008) and maternal TL (r = −264, p = 0.047), but not with paternal TL (p > 0.05). The ADHD inattentive dimension was not significant associated with TL in this study (p > 0.05). TL was shown to be a potential biomarker of the ADHD symptoms burden in families affected by this neurodevelopmental disorder. However, it is crucial that future studies investigating the rate of telomere attrition in relation to psychiatric problems to consider the strong determination of TL at birth by inheritance.

Heritability of telomere length in a study of long-lived families

Chromosomal telomere length shortens with repeated cell divisions. Human leukocyte DNA telomere length (LTL) has been shown to shorten during aging. LTL shortening has correlated with decreased longevity, dementia, and other age-associated processes. Because LTL varies widely between individuals in a given age group, it has been hypothesized to be a marker of biological aging. However, the principal basis for the variation of human LTL has not been established, although various studies have reported heritability. Here, we use a family-based study of longevity to study heritability of LTL in 3037 individuals. We show that LTL is shorter in older individuals, and in males, and has a high heritability (overall h(2) = 0.54). In the offspring generation, who are in middle-life, we find an ordinal relationship: persons more-closely-related to elderly probands have longer LTL than persons less-closely-related, who nonetheless have longer LTL than unrelated spouses of the offspring generation. These results support a prominent genetic underpinning of LTL. Elucidation of such genetic bases may provide avenues for intervening in the aging process.

Depression, anxiety and telomere length in young adults: evidence from the National Health and Nutrition Examination Survey

Telomere length has been hypothesized to be a marker of cumulative exposure to stress, and stress is an established cause of depression and anxiety disorders. The aim of this study was to examine the relationship between depression, anxiety and telomere length, and to assess whether this relationship is moderated by race/ethnicity, gender and/or antidepressant use. Data were from the 1999-2002 National Health and Nutrition Examination Survey. Telomere length was assessed using the quantitative PCR method of telomere length relative to standard reference DNA. Past-year major depression (MD), generalized anxiety disorder (GAD) and panic disorder (PD), as well as depressed affect and anxious affect, were assessed using the Composite International Diagnostic Inventory (N=1290). Multiple linear regression was used to assess the relationship between depression and anxiety disorders and telomere length. Among women, those with GAD or PD had shorter telomeres than those with no anxious affect (β: -0.07, P<0.01), but there was no relationship among men (β: 0.08, P>0.05). Among respondents currently taking an antidepressant, those with MD had shorter telomeres than those without (β: -0.26, P<0.05), but there was no association between MD and telomere length among those not using antidepressants (β: -0.00, P>0.05). Neither depressive nor anxiety disorders were directly associated with telomere length in young adults. There was suggestive evidence that pharmacologically treated MD is associated with shorter telomere length, likely reflecting the more severe nature of MD that has come to clinical attention.

Leukocyte telomere length and late-life depression

OBJECTIVE

Depressive disorders have been associated with increased risk for aging-related diseases, possibly as a consequence of accelerated cellular aging. Cellular aging, indexed by telomere length (TL) shortening, has been linked to depression in adults younger than 60 years; however, it remains unclear whether this is the case in late-life depression (age >60 years). The objective of this study was to assess differences in TL between persons with current late-life depression and never-depressed comparisons and to examine the association between characteristics of late-life depression and TL.

METHODS

In this cross-sectional study using the Netherlands Study of Depression in Older Persons, 355 persons with current late-life depression and 128 never-depressed comparisons, aged 60-93 years (mean age [SD]: 70.5 [7.4] years, 65% women), were recruited through primary care and mental healthcare. Late-life depression was established using a Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-based structured psychiatric interview. Leukocyte TL, expressed in base pairs (bp), was determined in fasting blood samples by performing quantitative polymerase chain reaction.

RESULTS

Mean TL did not differ between depressed persons (bp [SD]: 5,035 [431]) and never-depressed (bp [SD]: 5,057 [729]) comparisons. Further, TL was not associated with severity, duration, and age at onset of depression; comorbid anxiety disorders; anxiety symptoms; apathy severity; antidepressant use; benzodiazepine use; cognitive functioning; and childhood trauma.

CONCLUSION

Late-life depression was not associated with increased cellular aging. This absent association, which contradicts observations in younger adults, may be due to the potential larger heterogenic nature of late-life depression and lifetime cumulative exposure to other TL-damaging factors, possibly overruling effects of late-life depression.

The association between depression and leukocyte telomere length: a meta-analysis

BACKGROUND

Telomeres protect the ends of chromosomes, and shorter leukocyte telomeres are associated with poor health. Depression may be associated with the shortening of leukocyte telomeres. The present study set out to consolidate the varying effect sizes found so far in studies of depression and telomere length and to identify moderators of the relationship between depression and telomere length.

METHODS

A meta-analytic investigation of the relationship between depression and leukocyte telomere length used information from 21,040 participants.

RESULTS

A significant effect size, r = -.12, P < .001, indicated that depression was associated with shorter telomere length. Several variables significantly moderated effect size. Concurrent associations (k = 25) between depression and telomere length were significantly stronger than longitudinal associations (k = 5). Studies that used the Southern blot (k = 3) and fluorescent in situ hybridization (FISH; k = 2) assays to measure telomere length showed larger effect sizes than studies that used quantitative polymerase chain reaction (qPCR; k = 25). Finally, study reports that indicated that the telomere assays were conducted blind to depression level of participants (k = 11) had significantly lower effect sizes than those of other studies (k = 19).

CONCLUSIONS

The significant relationship between depression and shorter telomere length is consistent with a theoretical model positing that distress, such as experienced in depression, results in physiological changes leading to shortened telomeres.

Relations between depressive symptoms, anxiety, and T Wave abnormalities in subjects without clinically-apparent cardiovascular disease (from the Multi-Ethnic Study of Atherosclerosis [MESA])

The aim of this study was to test the hypothesis that depression and anxiety are associated with electrocardiographic (ECG) repolarization abnormalities in the Multi-Ethnic Study of Atherosclerosis (MESA), a cohort free of symptomatic cardiovascular disease. Depressive symptoms were assessed by using the Center for Epidemiologic Studies Depression Scale and trait anxiety symptoms by using the Spielberger State-Trait Anxiety Inventory; both were categorized according to uppermost quartile. T-wave inversions in ECG leads other than V1 to V3 were obtained from electrocardiograms obtained at rest during the baseline examination. Participants with major intraventricular conduction abnormalities and those taking antiarrhythmics, antidepressants, and/or antipsychotics were excluded. Logistic regression models were estimated with multivariable adjustment for traditional cardiovascular disease risk factors. Among 5,906 participants, elevated depressive symptoms were associated with increased odds of T-wave inversion after multivariable adjustment (odds ratio 2.02, 95% confidence interval 1.33 to 3.06, p = 0.001), whereas greater trait anxiety was associated with reduced odds of T-wave inversion (odds ratio 0.47, 95% confidence interval 0.29 to 0.77, p = 0.003). The divergent associations of depressive symptoms and trait anxiety with ECG T-wave inversions were similar in men and women, and these associations were present across the racial and ethnic subgroups (non-Hispanic white, African-American, Hispanic, and Chinese). In conclusion, symptoms of depression and anxiety were independently yet oppositely associated with ECG T-wave inversions. Negative emotions may have a differential impact on cardiovascular mortality through unique relations with cardiac repolarization.

Depressive symptoms and short telomere length are associated with increased mortality in bladder cancer patients

BACKGROUND

Depression is associated with an increased risk of mortality in patients with cancer; it has been hypothesized that depression-associated alterations in cell aging mechanisms, in particular, the telomere/telomerase maintenance system, may underlie this increased risk. We evaluated the association of depressive symptoms and telomere length to mortality and recurrence/progression in 464 patients with bladder cancer.

METHODS

We used the Center for Epidemiologic Studies Depression Scale (CES-D) and Structured Clinical Interview for DSM-IV Disorder (SCID) to assess current depressive symptoms and lifetime major depressive disorder (MDD), respectively, and telomere length was assessed from peripheral blood lymphocytes. Multivariate Cox regression was used to assess the association of depression and telomere length to outcomes and the joint effect of both. Kaplan-Meier plots and log-rank tests were used to compare survival time of subgroups by depression variables and telomere length.

RESULTS

Patients with depressive symptoms (CES-D ≥ 16) had a 1.83-fold [95% confidence interval (CI), 1.08-3.08; P = 0.024] increased risk of mortality compared with patients without depressive symptoms (CES-D < 16) and shorter disease-free survival time (P = 0.004). Patients with both depressive symptoms and lifetime history of MDD were at 4.88-fold (95% CI, 1.40-16.99; P = 0.013) increased risk compared with patients with neither condition. Compared to patients without depressive symptoms and long telomere length, patients with depressive symptoms and short telomeres exhibited a 4-fold increased risk of mortality (HR, 3.96; 95% CI, 1.86-8.41; P = 0.0003) and significantly shorter disease-free survival time (P < 0.001).

CONCLUSION

Short telomere length and depressive symptoms are associated with bladder cancer mortality individually and jointly.

IMPACT

Further investigation of interventions that impact depression and telomere length may be warranted in patients with cancer.

No association between mean telomere length and life stress observed in a 30 year birth cohort

Telomeres are specialised structures that cap the ends of chromosomes. They shorten with each cell division and have been proposed as a marker of cellular aging. Previous studies suggest that early life stressors increase the rate of telomere shortening with potential impact on disease states and mortality later in life. This study examined the associations between telomere length and exposure to a number of stressors that arise during development from the antenatal/perinatal period through to young adulthood. Participants were from the Christchurch Health and Development Study (CHDS), a New Zealand longitudinal birth cohort which has followed participants from birth until age 30. Telomere length was obtained on DNA from peripheral blood samples collected from consenting participants (n = 677) at age 28–30, using a quantitative PCR assay. These data were assessed for associations with 26 measures of life course adversity or stress which occurred prior to 25 years of age. No associations were found between telomere length measured at age 28–30 years and life course adversity or stress for specific measures and for the summary risk scores for each developmental domain. The correlations were very small ranging from −0.06 to 0.06 with a median of 0.01, and none were statistically significant. Our results in this well-studied birth cohort do not support prior reports of such associations, and underscore the need for more extensive replication of proposed links between stress and telomere biology in larger cohorts with appropriate phenotypic data.

Shorter telomeres with high telomerase activity are associated with raised allostatic load and impoverished psychosocial resources

Recent work has linked psychological stress with premature cellular aging as indexed by reduced leukocyte telomere length. The combination of shorter telomeres with high telomerase activity (TA) may be indicative of active cell stress. We hypothesized that older individuals characterized by shorter telomeres with high TA in unstimulated leukocytes would show signs of high allostatic load and low levels of protective psychosocial resources. We studied 333 healthy men and women aged 54-76 y who underwent laboratory testing in which we measured cardiovascular, neuroendocrine, and inflammatory responses to standardized mental stress tasks. The tasks elicited prompt increases in blood pressure (BP), heart rate, cortisol, and mediators of inflammation and reductions in heart rate variability, returning toward baseline levels following stress. However, men having shorter telomeres with high TA showed blunted poststress recovery in systolic BP, heart rate variability, and monocyte chemoattractant protein-1, together with reduced responsivity in diastolic BP, heart rate, and cortisol, in comparison to men with longer telomeres or men with shorter telomeres and low TA. Shorter telomeres with high TA were also associated with reduced social support, lower optimism, higher hostility, and greater early life adversity. These effects were independent of age, socioeconomic status, and body mass index. We did not observe differences among older women. Our findings suggest that active cell stress is associated with impaired physiological stress responses and impoverished psychosocial resources, reflecting an integration of cellular, systemic, and psychological stress processes potentially relevant to health in older men.

Genome wide association and linkage analyses identified three loci-4q25, 17q23.2, and 10q11.21-associated with variation in leukocyte telomere length: the Long Life Family Study

Leukocyte telomere length is believed to measure cellular aging in humans, and short leukocyte telomere length is associated with increased risks of late onset diseases, including cardiovascular disease, dementia, etc. Many studies have shown that leukocyte telomere length is a heritable trait, and several candidate genes have been identified, including TERT, TERC, OBFC1, and CTC1. Unlike most studies that have focused on genetic causes of chronic diseases such as heart disease and diabetes in relation to leukocyte telomere length, the present study examined the genome to identify variants that may contribute to variation in leukocyte telomere length among families with exceptional longevity. From the genome wide association analysis in 4,289 LLFS participants, we identified a novel intergenic SNP rs7680468 located near PAPSS1 and DKK2 on 4q25 (p = 4.7E-8). From our linkage analysis, we identified two additional novel loci with HLOD scores exceeding three, including 4.77 for 17q23.2, and 4.36 for 10q11.21. These two loci harbor a number of novel candidate genes with SNPs, and our gene-wise association analysis identified multiple genes, including DCAF7, POLG2, CEP95, and SMURF2 at 17q23.2; and RASGEF1A, HNRNPF, ANF487, CSTF2T, and PRKG1 at 10q11.21. Among these genes, multiple SNPs were associated with leukocyte telomere length, but the strongest association was observed with one contiguous haplotype in CEP95 and SMURF2. We also show that three previously reported genes-TERC, MYNN, and OBFC1-were significantly associated with leukocyte telomere length at p empirical < 0.05.

Leukocyte telomere length in mastocytosis: correlations with depression and perceived stress

BACKGROUND

Mastocytosisis a rare disease associated with chronic symptoms related to mast cell mediator release. Patients with mastocytosis display high level of negative emotionality such as depression and stress sensibility. Brain mast cells are mainly localized in the diencephalon, which is linked to emotion regulatory systems. Negative emotionality has been shown to be associated with telomere shortening. Taken together these observations led us to hypothesize that mast cells activity could be involved in both negative emotionality and telomere shortening in mastocytosis.

OBJECTIVE

To demonstrate a possible relationship between negative emotionality in mastocytosis and leukocytes telomere length.

METHODS

Leukocyte telomere length and telomerase activity were measured among mastocytosis patients and were correlated with perceived stress and depression assessed by the Beck Depression Inventory revised and the Perceived Stress Scale.

RESULTS

Mild-severe depression scores were frequent (78.9%) as well as high perceived stress (42.11%). Telomere length was correlated to perceived stress (r=0.77; p=0.0001) but not to depression in our population. Patients displaying Wild-type KIT significantly presented higher perceived stress levels. Patients with the D816VC KIT mutation who had high perceived stress scores displayed significantly shorter telomere but not if they had high depression scores.

CONCLUSION

These findings suggest that high perceived stress in mastocytosis could accelerate the rate of leukocytes telomere shortening. Since mastocytosis is, by definition, a mast cell mediated disease; these cells could be involved in this phenomenon. Mechanistic causal relationships between these parameters need to be investigated.

Telomere length is associated with sleep duration but not sleep quality in adults with human immunodeficiency virus

BACKGROUND AND STUDY OBJECTIVE

Telomere length provides an estimate of cellular aging and is influenced by oxidative stress and health behaviors such as diet and exercise. This article describes relationships between telomere length and sleep parameters that included total sleep time (TST), wake after sleep onset (WASO), and self-reported sleep quality in a sample of adults with chronic illness.

DESIGN AND PARTICIPANTS

Cross-sectional study of 283 adults (74% male, 42% Caucasian) infected with human immunodeficiency virus (HIV) while living in the San Francisco Bay area, CA, USA. Ages ranged from 22-77 y.

MEASUREMENTS AND RESULTS

TST and WASO were estimated with wrist actigraphy across 72 h; self-reported sleep quality was assessed with the Pittsburgh Sleep Quality Index. Relative telomere length (RTL) in leukocytes was estimated by quantitative polymerase chain reaction assays. Shorter RTL was associated with older age, and RTL was shorter in males than females. RTL was unrelated to HIV disease characteristics. RTL was not associated with WASO or self-reported sleep quality. Participants with at least 7 h sleep had longer RTL than those with less than 7 h, even after controlling for the effects of age, sex, race, education, body mass index, metabolic hormones (i.e., leptin, ghrelin, adiponectin, and resistin), depression and anxiety, and sleep quality.

CONCLUSION

Results suggest that sleep duration is associated with preserving telomere length in a population of human immunodeficiency virus-infected adults. Getting at least 7 hours of sleep at night may either protect telomeres from damage or restore them on a nightly basis.

Major depressive disorder and measures of cellular aging: an integrative review

Major depressive disorder (MDD) affects millions of individuals and causes significant suffering worldwide. It has been speculated that MDD is associated with accelerated aging-related biological and functional decline. To examine the accelerated aging hypothesis, one of the biomarkers under study is leukocyte telomeres, and specifically the measure of telomere length and telomerase activity. This review integrates findings from eleven human studies which evaluated telomere length and telomerase activity, in order to synthesize the state of the current science and to inform the development of new knowledge and enhance nursing research of depression using appropriate biobehavioral measures. Although preliminary, the findings from this integrated review suggest that there is evidence to support a conceptualization of depression as a stress-related condition in which telomeres shorten over time in relation to cumulative exposure to the chronic stress of depression. For the purposes of testing in future nursing research, visual representations of the theoretical connection between stress vulnerabilities, depression, and health outcomes and key moderators and mediators involved in this conceptualization are provided. The findings from this review and the conceptual framework provided may be a useful step towards advancing therapeutic nursing interventions for this debilitating chronic condition.

Relation between leukocyte telomere length and incident coronary heart disease events (from the 1995 Canadian Nova Scotia Health Survey)

Leukocyte telomere length has been proposed as a biomarker of cellular aging and atherosclerosis. The aim of this study was to determine whether leukocyte telomere length is independently associated with incident coronary heart disease (CHD) in the general population. Telomere length was measured using a polymerase chain reaction method for participants enrolled in the 1995 Nova Scotia Health Survey (NSHS95; n = 1,917). The primary end point was the first occurrence of a fatal or nonfatal CHD event. During a mean follow-up period of 8.7 years, 164 fatal or nonfatal CHD events occurred. Compared with participants in the longest tertile of telomere length, those in the middle and shortest tertiles had increased incidence of CHD events (6.2, 11.2, and 12.2 per 1,000 person-years, respectively). After adjustment for demographics, traditional risk factors, and inflammatory markers including high-sensitivity C-reactive protein, interleukin-6, and soluble intercellular adhesion molecule-1, those in the middle tertile had significantly elevated risk for incident CHD (hazard ratio 1.63, 95% confidence interval 1.07 to 2.51, p = 0.02) compared with the longest tertile, whereas the risk for those in the shortest tertile was nonsignificantly elevated (hazard ratio 1.25, 95% confidence interval 0.82 to 1.90, p = 0.30). In conclusion, these findings do not support a linear association between leukocyte telomere length and incident CHD risk in the general population.