Family history of depression is associated with younger age of onset in patients with recurrent depression

BACKGROUND

Genetic epidemiology data suggest that younger age of onset is associated with family history (FH) of depression. The present study tested whether the presence of FH for depression or anxiety in first-degree relatives determines younger age of onset for depression.

METHOD

A sample of 1022 cases with recurrent major depressive disorder (MDD) was recruited at the Max Planck Institute and at two affiliated hospitals. Patients were assessed using the Schedules for Clinical Assessment in Neuropsychiatry and questionnaires including demographics, medical history, questions on the use of alcohol and tobacco, personality traits and life events. Survival analysis and the Cox proportional hazard model were used to determine whether FH of depression signals earlier age of onset of depression.

RESULTS

Patients who reported positive FH had a significantly earlier age of onset than patients who did not report FH of depression (log-rank=48, df=1, p<0.0001). The magnitude of association of FH varies by age of onset, with the largest estimate for MDD onset before age 20 years (hazard ratio=2.2, p=0.0009), whereas FH is not associated with MDD for onset after age 50 years (hazard ratio=0.89, p=0.5). The presence of feelings of guilt, anxiety symptoms and functional impairment due to depressive symptoms appear to characterize individuals with positive FH of depression.

CONCLUSIONS

FH of depression contributes to the onset of depression at a younger age and may affect the clinical features of the illness.

Genetic and phenotypic stability of measures of neuroticism over 22 years

People meeting diagnostic criteria for anxiety or depressive disorders tend to score high on the personality scale of neuroticism. Studying this dimension of personality can therefore give insights into the etiology of important psychiatric disorders. Neuroticism can be assessed easily via self-report questionnaires in large population samples. We have examined the genetic and phenotypic stability of neuroticism, measured up to 4 times over 22 years, on different scales, on a data set of 4,999 families with over 20,000 individuals completing at least 1 neuroticism questionnaire. The neuroticism scales used were the Eysenck Personality Questionnaire revised (EPQ-R), the EPQ-R shortened form, and the NEO 5 factor inventory personality questionnaire. The estimates of heritability of the individual measures ranged from .26 +/- .04 to .36 +/- .03. Genetic, environmental, and phenotypic correlations averaged .91, .42, and .57 respectively. Despite the range in heritabilities, a more parsimonious 'repeatability model' of equal additive genetic variances and genetic correlations of unity could not be rejected. Use of multiple measures increases the effective heritability from .33 for a single measure to .43 for mean score because of the reduction in the estimate of the environmental variance, and this will increase power in genetic linkage or association studies of neuroticism.

A whole genome association study of neuroticism using DNA pooling

We describe a multistage approach to identify single nucleotide polymorphisms (SNPs) associated with neuroticism, a personality trait that shares genetic determinants with major depression and anxiety disorders. Whole genome association with 452 574 SNPs was performed on DNA pools from approximately 2000 individuals selected on extremes of neuroticism scores from a cohort of 88 142 people from southwest England. The most significant SNPs were then genotyped on independent samples to replicate findings. We were able to replicate association of one SNP within the PDE4D gene in a second sample collected by our laboratory and in a family-based test in an independent sample; however, the SNP was not significantly associated with neuroticism in two other independent samples. We also observed an enrichment of low P-values in known regions of copy number variations. Simulation indicates that our study had approximately 80% power to identify neuroticism loci in the genome with odds ratio (OR)>2, and approximately 50% power to identify small effects (OR=1.5). Since we failed to find any loci accounting for more than 1% of the variance, the heritability of neuroticism probably arises from many loci each explaining much less than 1%. Our findings argue the need for much larger samples than anticipated in genetic association studies and that the biological basis of emotional disorders is extremely complex.

Association of the serotonin transporter gene, neuroticism and smoking behaviours

Cigarette consumption and smoking cessation are influenced in part by genes. Personality traits have also been implicated in the aetiology of smoking. Neuroticism, a personality trait with a heritable component, correlates well with anxiety and depression, increasing the risk of being a smoker and decreasing the chance of smoking cessation. Several prior studies in non-British populations have given conflicting results as to whether some genetic polymorphisms affect the relationship between smoking and neuroticism. This study investigated the influence of serotonin transporter (5HTTLPR) genotypes on a composite measure of neuroticism and cigarette consumption/smoking cessation in a British population. Although neuroticism was significantly associated with cigarette consumption and smoking cessation, genotype did not affect this relationship. Our results do not support initial interest in utilising 5HTTLPR genotypes in combination with neuroticism ratings for predicting outcome in smoking cessation clinical settings.

[Polymorphisms of genes of rennin-angiotensine system and their correlation with psychological manifestations of birth stress]

Study of correlation of polymorphisms of genes of the rennin-angiotensine system--insertion-deletion (I/D) polymorphism of the angiotensine-converting enzime (ACE), and the polymorphism of angiotensinogen (AGT), consisting in submission of T into C in the 704 position (M235T)--with various characteristics of psychological functioning and clinical characteristics in women giving birth, was conducted. The group consisted of 56 young female Ss, without chronic diseases in the anamnesis, no complication in the course of pregnancy, birth normal and timely, state of the child normal in all cases. Basing on factor analysis of 7 psychological induces, providing integral assessment of state of the Ss in the course la late pregnancy, giving birth, and the immediately following post partum period, statistically reliable correlation between such first-rate psychological process as creativity, and polymorphism of the gene of angiotensinogene, was demonstrated, as well as difference in distribution of genotypes between the group of women giving birth, and general population. Statistically relevant correlation between presence of the deletion (D) allele of the ACE gene, and heightened level of neuroticization, reported by us earlier, was observed in this case, as well. No significant links between religiosity/spirituality, and genetic data was found. These results are in concordance with present-day views concerning the role of the rennin-angiotensine system in the providing of active adaptation to stressful conditions; they tend to provide fresh outlook upon the comparative study of input of heredity, and education, into the ontogenesis of higher psychological functions in normal humans.

Association between broadly defined bulimia nervosa and drug use disorders: common genetic and environmental influences

OBJECTIVE

Previous research has shown an association between bulimia (BN) and drug use disorders (DUD). The purpose of the present study was to investigate possible influences on the comorbidity between BN and DUD.

METHOD

Participants included 490 monozygotic and 354 dizygotic female twins and 930 females from opposite sex pairs. Multiple logistic regression analyses were used to test shared correlates and mediators. Bivariate twin analyses were used to investigate the contribution of genes and environment to the correlation between BN and DUD.

RESULTS

Depression, neuroticism, and childhood sexual abuse (CSA) mediated the association between BN and DUD regardless of which disorder was used as the dependent variable. Analyses also indicated genetic and nonshared environmental overlap between BN and DUD.

CONCLUSION

The association between BN and DUD is due mostly to overlapping genetic influences with a smaller contribution from nonshared environment. Depression, neuroticism, and CSA are likely important shared correlates.

Religious upbringing and neuroticism in Dutch twin families

Evidence for a relation between neuroticism and religion is scarce and inconsistent. The aims of the present study were to determine the association of religious upbringing with adult neuroticism scores and to examine the effect of religious upbringing on the heritability of neuroticism. As part of a longitudinal survey of twin families from the Netherlands Twin Register, data were collected on neuroticism and religious upbringing. Restricting the sample to persons aged 25 and over resulted in a sample of 4369 twins and 1304 siblings from 2698 families. Religious upbringing was significantly associated with neuroticism; in both men and women neuroticism levels were lower in those who had received a religious upbringing. There were no sex or twin sibling differences in neuroticism variances and covariances. Structural equation modeling showed differences in heritability between those with and without religious upbringing. In the group with religious upbringing, variation in neuroticism was determined for 41% by additive genetic factors and for the remaining 59% by unique environmental factors. In the group who had not received a religious upbringing, variation in neuroticism was determined for 55% by genetic factors, with evidence for both additive and nonadditive factors, and for the remaining 45% by unique environmental influences. In conclusion, having received a religious upbringing is associated with lower neuroticism scores and a lower heritability in adulthood.

A longitudinal study of personality and major depression in a population-based sample of male twins

BACKGROUND

The relationship between personality and psychiatric illness is complex. It is not clear whether one directly causes the other.

METHOD

In a population-based sample of male twins (n=3030), we attempted to predict major depression (MD) from neuroticism (N) and extraversion (E) and vice versa, to evaluate the causal, scar, state, and prodromal hypotheses. In a longitudinal, structural equation twin model, we decomposed the covariation between N and MD into (a) genetic and environmental factors that are common to both traits, as well as specific to each one and (b) direct causal effects of N at time 1 on subsequent MD, as well as between MD and subsequent N.

RESULTS

E was negatively correlated with lifetime and one-year prevalence of MD. N predicted the new onset of MD, and was predicted by both current and past MD. It did not predict the time to onset of MD. All of the covariation between N and MD was due to additive genetic and individual-specific environmental factors shared by both traits and a direct causal path between MD and N assessed later. No genetic factors were unique to either trait.

CONCLUSIONS

In men, N may be a vulnerability factor for MD but does not cause it directly. However, MD may have a direct causal effect on N. The genetic overlap between N and MD in men may be greater than in women.

Interrelationship of childhood trauma, neuroticism, and depressive phenotype

Both childhood trauma (CT) and genetic factors contribute to the pathophysiology of depression. We studied the relationship of CT to age of onset (AO) of depression, personality traits, and expression of symptom dimensions in 324 adults with recurrent unipolar depression. Subjects received structured psychiatric interviews and completed CT, depressive symptom, and personality rating questionnaires. Experience of at least one type of trauma was reported by 79.9% of subjects, and the most common forms of trauma were physical neglect, emotional abuse, and emotional neglect. There was an earlier AO of depression in the groups that reported CT compared to those that reported none, with earliest AO occurring in those who had experienced the highest levels of CT. There were no significant correlations between overall CT scores and neuroticism or extraversion. Total CT was a significant (P=.008) predictor of the Mood symptom dimension, mostly accounted for by emotional abuse (P=.019), and physical neglect predicted the Anxiety symptom dimension (P=.002). All types of CT are commonly reported in individuals with depression, and emotional abuse and physical neglect, though previously less well identified, appear to have an important role in the pathogenesis of depressive disorders. The effect of CT on individuals with an underlying genetic vulnerability to depression may result in differences in depressive phenotype characterized by earlier AO of depression and the expression of specific depressive symptom dimensions.

Anxiety and comorbid measures associated with PLXNA2

CONTEXT

Reduction in adult neurogenesis has been proposed as a mechanism for onset of depression. Semaphorins and their coreceptors, plexins, have been implicated in nervous system development and in adult neurogenesis. A recent genomewide association study of schizophrenia identified a variant of the gene encoding plexin A2 (PLXNA2) to be most consistently associated across study samples. Common genetic liabilities have been reported between psychiatric and psychological measures, but few examples exist of common genetic variants.

OBJECTIVE

To perform a genetic association study between 6 single nucleotide polymorphisms from the PLXNA2 gene (rs3736963, rs2767565, rs752016, rs1327175, rs2478813, and rs716461) and anxiety, depression, neuroticism, and psychological distress.

DESIGN

Extreme discordant and concordant siblings.

SETTING

Australia.

PARTICIPANTS

Study participants were selected with respect to extreme neuroticism scores from a population cohort of 18 742 twin individuals and their siblings. The participants and their parents (if blood or buccal samples were available) were genotyped, for a total of 2854 genotyped individuals from 990 families. Of these, 624 individuals with a diagnosis of anxiety or depression from 443 families were used in the association analysis.

MAIN OUTCOME MEASURES

All the participants completed the Composite International Diagnostic Interview, the 23-item Neuroticism scale of the revised Eysenck Personality Questionnaire, and the 10-item Kessler Psychological Distress Scale. Diagnoses of DSM-IV depression and anxiety were determined from the Composite International Diagnostic Interview.

RESULTS

There was evidence of an allelic association between rs2478813 (and other single nucleotide polymorphisms correlated with it) and anxiety, depression, neuroticism, and psychological distress; the association with anxiety is significant after Bonferroni correction for multiple testing (empirical P<.001). The mouse ortholog of PLXNA2 is located in a highly significant linkage region previously reported for anxiety in mice.

CONCLUSION

PLXNA2 is a candidate for causal variation in anxiety and in other psychiatric disorders through its comorbidity with anxiety.

A genome-wide linkage analysis for the personality trait neuroticism in the Irish affected sib-pair study of alcohol dependence

Neuroticism is a personality trait which reflects individual differences in emotional stability and vulnerability to stress and anxiety. Consistent evidence shows substantial genetic influences on variation in this trait. The present study seeks to identify regions containing susceptibility loci for neuroticism using a selected sib-pair sample from Ireland. Using Merlin regress, we conducted a 4 cM whole-genome linkage analysis on 714 sib-pairs. Evidence for linkage to neuroticism was found on chromosomes 11p, 12q, and 15q. The highest linkage peak was on 12q at marker D12S1638 with a Lod score of 2.13 (-log p = 2.76, empirical P-value <0.001). Our data also support gender specific loci for neuroticism, with male specific linkage regions on chromosomes 1, 4, 11, 12, 15, 16, and 22, and female specific linkage regions on chromosomes 2, 4, 9, 12, 13, and 18. Some genome regions reported in the present study replicate findings from previous linkage studies of neuroticism. These results, together with prior studies, indicate several potential regions for quantitative trait loci for neuroticism that warrant further study.

Genetic variation in the hypothalamic?pituitary?adrenocortical axis regulatory factor, T-box 19, and the angry/hostility personality trait

Neurotic personality traits are important factors in several psychiatric disorders and suicidal behavior. Here, we have investigated the existence of potential relationships between neurotic personality traits and genetic variation. Non-suicidal parents derived from trios (suicide attempter and both parents) and non-suicidal volunteers, examined by the Neuroticism, Extraversion and Openness (NEO) Personality Inventory - Revised (NEO PI-R), were divided into screening and replication samples. The screening sample (n= 127) was used to select potential relationships between neurotic personality traits and genetic variation among 130 single nucleotide polymorphisms (SNPs). Screening (analysis of variance) with regard to the personality dimension neuroticism indicated potential relationships at three different loci. More detailed analysis of these three SNPs at NEO PI-R facet level indicated four potential relationships. T-test analysis in the replication sample (n= 617) was used to retest the relationships indicated during screening. One of those relationships was confirmed in the replication sample (P= 0.0052; Bonferroni correction), indicating that genetic variation at the human T-box 19 (TBX19) locus is related to the personality trait angry/hostility. Furthermore, using analysis of haplotypes among trios by transmission disequilibrium test and its extension, the family-based association test, overtransmission of a haplotype GAC at the TBX19 locus was associated with increased angry/hostility scores among suicide attempters (P= 0.009; Bonferroni correction). This is to our knowledge the first report on the association of the angry hostility personality trait with genetic variation at the TBX19 locus, an important regulator of the hypothalamic-pituitary-adrenocortical axis.

A GENOTYPE-ENDOPHENOTYPE-PHENOTYPE PATH MODEL OF DEPRESSED MOOD: INTEGRATING COGNITIVE AND EMOTIONAL MARKERS

AIMS

Following an integrative neuroscience perspective, we propose that cognitive and emotional functions are integrally linked, and that genetic polymorphisms which impact upon neural processes may have complementary effects on these functions. The brain-derived neurotrophic factor (BDNF) 66Met allele may contribute to both cognitive and emotional aspects of the depression phenotype.

METHODS

In 374 nonclinical subjects, BDNF genotype differences in task-related ERPs, emotion, memory, and EEG cortical arousal were examined.

RESULTS

Using path modeling, higher negative affect in Met homozygotes was predicted by slow-wave EEG via the mediating effects of neuroticism. Both negative affect and working memory deficits were predicted by disturbances in emotion- and cognitive-related ERPs. This model held across groups with varying levels of depressed mood.

DISCUSSION

Since impairments in emotion and working memory are core features of major depression, the BDNF Met allele may contribute to vulnerability for this disorder. An integrative approach in which genotypes are considered in combination with brain function and behavioral measures may be important in identifying profile markers of depression.

INTEGRATIVE SIGNIFICANCE

This study directly demonstrates that cognitive and emotional neural networks are not parallel independent systems, but rather highly integrated with effects on both cognitive performance and emotional behavior.

The sources of co-morbidity between major depression and generalized anxiety disorder in a Swedish national twin sample

BACKGROUND

Prior studies report high levels of co-morbidity between major depression (MD) and generalized anxiety disorder (GAD) and suggest that these disorders are closely related genetically. The personality trait of neuroticism (N) is substantially correlated with risk for MD and GAD.

METHOD

Bivariate twin models were applied to lifetime diagnoses of modified DSM-IV diagnosis of MD and GAD obtained at personal interview in 1998-2003 with 37296 twins from the population-based Swedish Twin Registry. A trivariate Cholesky model with N, MD and GAD was applied to a subset (23280 members of same-sex twin pairs) who completed a self-report questionnaire assessing N in 1972-1973.

RESULTS

In the best-fit bivariate model, the genetic correlation between MD and GAD was estimated at +1.00 in females and +0.74 in males. Individual-specific environmental factors were also shared between the two disorders with an estimated correlation of +0.59 in males and +0.36 in females. In the best-fit trivariate Cholesky model, genetic factors indexed by N impacted equally on risk for MD and GAD in males and females. However, in both sexes, genetic risk factors indexed by N contributed only around 25% to the genetic correlation between MD and GAD.

CONCLUSION

Genetic risk factors for lifetime MD and GAD are strongly correlated, with higher correlations in women than in men. Although genetic risk factors indexed by the personality trait of N contribute substantially to risk for both MD and GAD, the majority of genetic covariance between the two disorders results from factors not shared with N.

Family history of alcoholism and the stability of personality in young adulthood

The authors examined the magnitude and durability of personality differences related to family history of alcoholism (FH) and the development of alcohol use disorders (AUDs) in late adolescence and early adulthood. Data were taken from a longitudinal sample (N = 487; approximately half FH-positive [+]) who completed the Eysenck Personality Questionnaire (H. J. Eysenck & S. B. G. Eysenck, 1975) at 3 points spanning 11 years (participants were 18 years old at baseline). Hierarchical linear analyses showed that FH+ participants had higher levels of neuroticism and psychoticism over the study period, independent of AUD. Despite relatively large mean decreases in neuroticism (as well as extraversion), the magnitude of the between-groups differences found at age 18 were maintained over the next decade. These changes thus reflect stable underlying differences in personality and not artifacts of higher rates of AUDs in FH+ individuals, recently living in an alcoholic home, vulnerability to the developmental challenge of leaving home, and/or a developmental lag.

The genetic relationship between neuroticism and autonomic function in female twins

BACKGROUND

Neuroticism is widely used as an explanatory concept in etiological research of psychopathology. In order to clarify what neuroticism actually represents, we investigated the genetic association between neuroticism and cardiovascular measures.

METHOD

In 125 female twin pairs (18-30 years), electrocardiogram and continuous finger blood pressure were assessed during two rest and two mental stress conditions. Mean values for baroreflex sensitivity (BRS), heart rate variability (HRV) and inter-beat interval (IBI) were calculated for each condition. Neuroticism was assessed by multiple questionnaires. Multivariate genetic model-fitting analyses were used to investigate the genetic correlation between latent neuroticism and the cardiovascular autonomic nervous system (ANS) measures.

RESULTS

Neuroticism was negatively correlated to BRS and HRV. Neuroticism was not correlated to IBI. For BRS, this phenotypical relation was entirely determined by shared genetic influences. For HRV, the genetic contribution to the phenotypical correlation was not significant, but the proportions of explained covariance showed a trend of more genetic than environmental influences on the phenotypical relationship.

CONCLUSIONS

High neuroticism is associated with a deregulated ANS. Pleiotropic genetic effects may be partly responsible for this effect.

Family Based Association Analyses between the Serotonin Transporter Gene Polymorphism (5-HTTLPR) and Neuroticism, Anxiety and Depression

We studied the association between the short/long promotor-based length polymorphism of the serotonin transporter gene (5-HTTLPR) and neuroticism, anxiety and depression. Subjects included twins, their siblings and parents from the Netherlands Twin Register (559 parents and 1,245 offspring). Subjects had participated between one and five times in a survey study measuring neuroticism, anxiety and depression. Offspring of these families were also approached to participate in a psychiatric interview diagnosing DSM-IV major depression. Within-family and total association between 5-HTTLPR and these traits were tested. Only three of the 36 tests showed a significant effect of 5-HTTLPR (P<0.05). These effects were in opposite directions, i.e. both negative and positive regression coefficients were found for the s allele. No additive effect of the s allele was found for DSM-IV depression. Our results strongly suggest that there is no straightforward association between 5-HTTLPR and neuroticism, anxiety and depression.

Personality and Major Depression

CONTEXT

Prior studies suggest that the personality traits of neuroticism and extroversion may be related to the liability to major depression (MD).

OBJECTIVE

To clarify the magnitude and nature of the association between neuroticism and extroversion and the risk for MD.

DESIGN

Longitudinal population-based twin cohort.

SETTING

General community.

PARTICIPANTS

A total of 20 692 members of same-sex twin pairs from the population-based Swedish Twin Registry who completed a self-report questionnaire assessing neuroticism and extroversion in 1972 and 1973 and were personally interviewed for lifetime history of MD more than 25 years later.Main Outcome Measure Lifetime history of modified DSM-IV MD.

RESULTS

Levels of neuroticism strongly predicted the risks for both lifetime and new-onset MD. Twin modeling indicated that the association between neuroticism and MD resulted largely from shared genetic risk factors, with a genetic correlation of +0.46 to +0.47. Levels of extroversion were weakly and inversely related to the risks for lifetime and new-onset MD. This effect disappeared when we controlled for the level of neuroticism. Twin modeling produced similar results.

CONCLUSIONS

Results from both longitudinal and genetic analyses support the hypothesis that neuroticism strongly reflects the liability to MD. This association arises largely because neuroticism indexes the genetic risk for depressive illness. However, substantial proportions of the genetic vulnerability to MD are not reflected in neuroticism. By contrast, extroversion is only weakly related to risk for MD.

Association between glutamic acid decarboxylase genes and anxiety disorders, major depression, and neuroticism

Abnormalities in the gamma-aminobutyric acid (GABA) neurotransmitter system have been noted in subjects with mood and anxiety disorders. Glutamic acid decarboxylase (GAD) enzymes synthesize GABA from glutamate, and, thus, are reasonable candidate susceptibility genes for these conditions. In this study, we examined the GAD1 and GAD2 genes for their association with genetic risk across a range of internalizing disorders. We used multivariate structural equation modeling to identify common genetic risk factors for major depression, generalized anxiety disorder, panic disorder, agoraphobia, social phobia and neuroticism (N) in a sample of 9270 adult subjects from the population-based Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. One member from each twin pair for whom DNA was available was selected as a case or control based on scoring at the extremes of the genetic factor extracted from the analysis. The resulting sample of 589 cases and 539 controls was entered into a two-stage association study in which candidate loci were screened in stage 1, the positive results of which were tested for replication in stage 2. Several of the six single-nucleotide polymorphisms tested in the GAD1 region demonstrated significant association in both stages, and a combined analysis in all 1128 subjects indicated that they formed a common high-risk haplotype that was significantly over-represented in cases (P=0.003) with effect size OR=1.23. Out of 14 GAD2 markers screened in stage 1, only one met the threshold criteria for follow-up in stage 2. This marker, plus three others that formed significant haplotype combinations in stage 1, did not replicate their association with the phenotype in stage 2. Subject to confirmation in an independent sample, our study suggests that variations in the GAD1 gene may contribute to individual differences in N and impact susceptibility across a range of anxiety disorders and major depression.

The normalcy of neurosis: evolutionary origins of obsessive-compulsive disorder and related behaviors

One of the most curious questions plaguing subscribers of evolutionary theory is how natural selection's fine-tuned editing function could allow disease to persist. For evolutionary psychiatrists, the existence of psychopathology is thus perplexing. To illustrate a potential answer to one instance of this broad question, we examine the correlates of obsessive-compulsive disorder (OCD) within our normal repertoire of thought and action. The evidence presents a picture of OCD as a dysregulation of normal behaviors and mental states throughout the course of human development. We speculate that such correspondence may be more than a coincidence and that OCD is a consequence of a dysregulation of the neural circuits that are crucially involved in threat detection and harm avoidance. These neural systems are also likely to underlie aspects of religious experience and ritual as well as the wonders of romantic and early parental love.

Neuroticism mediates the association of the serotonin transporter gene with lifetime major depression

BACKGROUND AND OBJECTIVES

An association between a polymorphism in the serotonin transporter gene (5HTT-LPR) and the personality trait of neuroticism has been reported. We sought to address the question of whether trait neuroticism mediates the putative association between this polymorphism and lifetime major depression in adults drawn from the general population.

METHODS

Two hundred and fifty-one participants completed the Eysenck Personality Questionnaire and an adapted version of the depression section of the Structured Clinical Interview for DSM-III-R diagnosis, modified for implementation by a self-report questionnaire. A path method was applied to assess the mediator effect of neuroticism on the association between 5HTT-LPR genotype and lifetime major depression.

RESULTS

5HTT-LPR genotype was significantly associated with both neuroticism (p=0.02) and lifetime major depression (p=0.04), and neuroticism with lifetime major depression (p<0.001). Neuroticism accounted for 42.3% of the effect of 5HTT-LPR genotype on lifetime major depression, indicating possible mediation (p<0.001).

CONCLUSIONS

These results suggest that neuroticism mediates the association between 5HTT-LPR genotype and lifetime major depression, consistent with models of the aetiology of depression which suggest that anxiety-related personality traits represent a substantial risk factor for affective disorder.

The genetic architecture of neuroticism in 3301 Dutch adolescent twins as a function of age and sex: a study from the Dutch twin register

The objective of this study was to estimate the magnitude of genetic and environmental influences to variation in adolescent neuroticism as a function of age and sex. Neuroticism was assessed using the Amsterdamse Biografische Vragenlijst (ABV): a self-report personality instrument similar in content to the Eysenck Personality Questionnaire. Genetic modeling procedures, including age as modifier, were fitted to the total sample of 3301 Dutch adolescent twins aged 12 to 17 years (mean age 15.5). Significant influences of additive genetic factors (.59, 95% confidence intervals [CI] .54-.63) and unshared environmental factors (.41, 95% CI .37-.45) were found. Our data did not support a role of shared environment. Results showed that different genes may influence variation in neuroticism between girls and boys. No interaction was found between the variance components and age. Results generally support prior findings in adults and young children that neuroticism is influenced principally by additive genetic and unique environmental factors. The magnitude of the genetic component appears higher in the present sample of adolescents than in most studies of adults. The present study suggests that, in adolescence, different genes are expressed in boys and girls.

A twin study of lifetime Generalized Anxiety Disorder (GAD) in older adults: genetic and environmental influences shared by neuroticism and GAD

The nature of Generalized Anxiety Disorder (GAD) and worry across the lifespan remains incompletely understood. We investigated genetic and environmental influences on GAD and the proportion of genetic and environmental variation in GAD that is shared with neuroticism in older adult twins. Participants included 1618 monozygotic and 2291 same-sexed dizygotic twin pairs from the Swedish Twin Registry aged 55 to 74. Participants provided personality information in 1973 and also participated in a telephone screening between 1998 and 2002 that included an assessment for lifetime GAD. Univariate biometric models indicated that both GAD and neuroticism were moderately heritable (.27 and .47, respectively), while the balance of variation reflected environmental factors unique to the individual. Bivariate analyses indicated that approximately one third of the genetic influences on GAD were in common with genetic influences on neuroticism, while individual specific environmental influences were virtually unshared between GAD and neuroticism. Analyses of sex effects suggested that men and women differed in the frequency of lifetime GAD and level of neuroticism; however, no sex differences for genetic and environmental influences for either trait were identified.