Robust symptom networks in recurrent major depression across different levels of genetic and environmental risk

BACKGROUND

Genetic risk and environmental adversity-both important risk factors for major depression (MD)-are thought to differentially impact on depressive symptom types and associations. Does heterogeneity in these risk factors result in different depressive symptom networks in patients with MD?

METHODS

A clinical sample of 5784 Han Chinese women with recurrent MD were interviewed about their depressive symptoms during their lifetime worst episode of MD. The cases were classified into subgroups based on their genetic risk for MD (family history, polygenic risk score, early age at onset) and severe adversity (childhood sexual abuse, stressful life events). Differences in MD symptom network structure were statistically examined for these subgroups using permutation-based network comparison tests.

RESULTS

Although significant differences in symptom endorsement rates were seen in 18.8% of group comparisons, associations between depressive symptoms were similar across the different subgroups of genetic and environmental risk. Network comparison tests showed no significant differences in network strength, structure, or specific edges (P-value > 0.05) and correlations between edges were strong (0.60-0.71).

LIMITATIONS

This study analyzed depressive symptoms retrospectively reported by severely depressed women using novel statistical methods. Future studies are warranted to investigate whether similar findings hold in prospective longitudinal data, less severely depressed patients, and men.

CONCLUSIONS

Similar depressive symptom networks for MD patients with a higher or lower genetic or environmental risk suggest that differences in these etiological influences may produce similar symptom networks downstream for severely depressed women.

Do DSM-5 Section II personality disorders and Section III personality trait domains reflect the same genetic and environmental risk factors?

BACKGROUND

DSM-5 includes two conceptualizations of personality disorders (PDs). The classification in Section II is identical to the one found in DSM-IV, and includes 10 categorical PDs. The Alternative Model (Section III) includes criteria for dimensional measures of maladaptive personality traits organized into five domains. The degree to which the two conceptualizations reflect the same etiological factors is not known.

METHODS

We use data from a large population-based sample of adult twins from the Norwegian Institute of Public Health Twin Panel on interview-based DSM-IV PDs and a short self-report inventory that indexes the five domains of the DSM-5 Alternative Model plus a domain explicitly targeting compulsivity. Schizotypal, Paranoid, Antisocial, Borderline, Avoidant, and Obsessive-compulsive PDs were assessed at the same time as the maladaptive personality traits and 10 years previously. Schizoid, Histrionic, Narcissistic, and Dependent PDs were only assessed at the first interview. Biometric models were used to estimate overlap in genetic and environmental risk factors.

RESULTS

When measured concurrently, there was 100% genetic overlap between the maladaptive trait domains and Paranoid, Schizotypal, Antisocial, Borderline, and Avoidant PDs. For OCPD, 43% of the genetic variance was shared with the domains. Genetic correlations between the individual domains and PDs ranged from +0.21 to +0.91.

CONCLUSION

The pathological personality trait domains, which are part of the Alternative Model for classification of PDs in DSM-5 Section III, appears to tap, at an aggregate level, the same genetic risk factors as the DSM-5 Section II classification for most of the PDs.

Contributions of Genes and Environment to Developmental Change in Alcohol Use

The precise nature of how genetic and environmental risk factors influence changes in alcohol use (AU) over time has not yet been investigated. Therefore, the aim of the present study is to examine the nature of longitudinal changes in these risk factors to AU from mid-adolescence through young adulthood. Using a large sample of male twins, we compared five developmental models that each makes different predictions regarding the longitudinal changes in genetic and environmental risks for AU. The best-fitting model indicated that genetic influences were consistent with a gradual growth in the liability to AU, whereas unique environmental risk factors were consistent with an accumulation of risks across time. These results imply that two distinct processes influence adolescent AU between the ages of 15-25. Genetic effects influence baseline levels of AU and rates of change across time, while unique environmental effects are more cumulative.

The Genetic and Environmental Sources of Resemblance Between Normative Personality and Personality Disorder Traits

Recent work has suggested a high level of congruence between normative personality, most typically represented by the "big five" factors, and abnormal personality traits. In 2,293 Norwegian adult twins ascertained from a population-based registry, the authors evaluated the degree of sharing of genetic and environmental influences on normative personality, assessed by the Big Five Inventory (BFI), and personality disorder traits (PDTs), assessed by the Personality Inventory for DSM-5-Norwegian Brief Form (PID-5-NBF). For four of the five BFI dimensions, the strongest genetic correlation was observed with the expected PID-5-NBF dimension (e.g., neuroticism with negative affectivity [+], conscientiousness with disinhibition [-]). However, neuroticism, conscientiousness, and agreeableness had substantial genetic correlations with other PID-5-NBF dimensions (e.g., neuroticism with compulsivity [+], agreeableness with detachment [-]). Openness had no substantial genetic correlations with any PID-5-NBF dimension. The proportion of genetic risk factors shared in aggregate between the BFI traits and the PID-5-NBF dimensions was quite high for conscientiousness and neuroticism, relatively robust for extraversion and agreeableness, but quite low for openness. Of the six PID-5-NBF dimensions, three (negative affectivity, detachment, and disinhibition) shared, in aggregate, most of their genetic risk factors with normative personality traits. Genetic factors underlying psychoticism, antagonism, and compulsivity were shared to a lesser extent, suggesting that they are influenced by etiological factors not well indexed by the BFI.

A longitudinal, population-based twin study of avoidant and obsessive-compulsive personality disorder traits from early to middle adulthood

BACKGROUND

The phenotypic stability of avoidant personality disorder (AVPD) and obsessive-compulsive personality disorder (OCPD) has previously been found to be moderate. However, little is known about the longitudinal structure of genetic and environmental factors for these disorders separately and jointly, and to what extent genetic and environmental factors contribute to their stability.

METHOD

AVPD and OCPD criteria were assessed using the Structured Interview for DSM-IV Personality in 2793 young adult twins (1385 pairs, 23 singletons) from the Norwegian Institute of Public Health Twin Panel at wave 1 and 2282 (986 pairs, 310 singletons) of these on average 10 years later at wave 2. Longitudinal biometric models were fitted to AVPD and OCPD traits.

RESULTS

For twins who participated at both time-points, the number of endorsed sub-threshold criteria for both personality disorders (PDs) decreased 31% from wave 1 to wave 2. Phenotypic correlations between waves were 0.54 and 0.37 for AVPD and OCPD, respectively. The heritability estimates of the stable PD liabilities were 0.67 for AVPD and 0.53 for OCPD. The genetic correlations were 1.00 for AVPD and 0.72 for OCPD, while the unique environmental influences correlated 0.26 and 0.23, respectively. The correlation between the stable AVPD and OCPD liabilities was 0.39 of which 63% was attributable to genetic influences. Shared environmental factors did not significantly contribute to PD variance at either waves 1 or 2.

CONCLUSION

Phenotypic stability was moderate for AVPD and OCPD traits, and genetic factors contributed more than unique environmental factors to the stability both within and across phenotypes.

A longitudinal twin study of borderline and antisocial personality disorder traits in early to middle adulthood

BACKGROUND

Antisocial personality disorder (ASPD) and borderline personality disorder (BPD) share genetic and environmental risk factors. Little is known about the temporal stability of these etiological factors in adulthood.

METHOD

DSM-IV criteria for ASPD and BPD were assessed using structured interviews in 2282 Norwegian twins in early adulthood and again approximately 10 years later. Longitudinal biometric models were used to analyze the number of endorsed criteria.

RESULTS

The mean criterion count for ASPD and BPD decreased 40% and 28%, respectively, from early to middle adulthood. Rank-order stability was 0.58 for ASPD and 0.45 for BPD. The best-fitting longitudinal twin model included only genetic and individual-specific environmental factors. Genetic effects, both those shared by ASPD and BPD, and those specific to each disorder remained completely stable. The unique environmental effects, however, changed substantially, with a correlation across time of 0.19 for the shared effects, and 0.39 and 0.15, respectively, for those specific to ASPD and BPD. Genetic effects accounted for 71% and 72% of the stability over time for ASPD and BPD, respectively. The genetic and environmental correlations between ASPD and BPD were 0.73, and 0.43, respectively, at both time points.

CONCLUSION

ASPD and BPD traits were moderately stable from early to middle adulthood, mostly due to genetic risk factors which did not change over the 10-year assessment period. Environmental risk factors were mostly transient, and appear to be the main source of phenotypic change. Genetic liability factors were, to a large extent, shared by ASPD and BPD.

Identification and validation of mixed anxiety-depression

BACKGROUND

Mixed anxiety-depression (MAD) has been under scrutiny to determine its potential place in psychiatric nosology. The current study sought to investigate its prevalence, clinical characteristics, course and potential validators.

METHOD

Restricted latent-class analyses were fit to 12-month self-reports of depression and anxiety symptom criteria in a large population-based sample of twins. Classes were examined across an array of relevant indicators (demographics, co-morbidity, adverse life events, clinical significance and twin concordance). Longitudinal analyses investigated the stability of, and transitions between, these classes for two time periods approximately 1.5 years apart.

RESULTS

In all analyses, a class exhibiting levels of MAD symptomatology distinctly above the unaffected subjects yet having low prevalence of either major depression (MD) or generalized anxiety disorder (GAD) was identified. A restricted four-class model, constraining two classes to have no prior disorder history to distinguish residual or recurrent symptoms from new onsets in the last year, provided an interpretable classification: two groups with no prior history that were unaffected or had MAD and two with prior history having relatively low or high symptom levels. Prevalence of MAD was substantial (9-11%), and subjects with MAD differed quantitatively but not qualitatively from those with lifetime MD or GAD across the clinical validators examined.

CONCLUSIONS

Our findings suggest that MAD is a commonly occurring, identifiable syndromal subtype that warrants further study and consideration for inclusion in future nosologic systems.

The similarity of the structure of DSM-IV criteria for major depression in depressed women from China, the United States and Europe

BACKGROUND

Do DSM-IV diagnostic criteria for major depression (MD) in Chinese and Western women perform in a similar manner?

METHOD

The CONVERGE study included interview-based assessments of women of Han Chinese descent with treated recurrent MD. Using Mplus software, we investigated the overall degree of between-sample measurement invariance (MI) for DSM-IV diagnostic criteria for MD in the CONVERGE sample and samples selected from four major Western studies from the USA and Europe matched to the inclusion criteria of CONVERGE. These analyses were performed one pair at a time. We then compared the results from CONVERGE paired with Western samples to those obtained when examining levels of MI between pairs of the Western samples.

RESULTS

Assuming a single factor model for the nine diagnostic criteria for MD, the level of MI based on global fit indexes observed between the CONVERGE and the four Western samples was very similar to that seen between the Western samples. Comparable results were obtained when using a two-factor structure for MI testing when applied to the 14 diagnostic criteria for MD disaggregated for weight, appetite, sleep, and psychomotor changes.

CONCLUSIONS

Despite differences in language, ethnicity and culture, DSM criteria for MD perform similarly in Chinese women with recurrent MD and comparable subjects from the USA and Europe. The DSM criteria for MD may assess depressive symptoms that are relatively insensitive to cultural and ethnic differences. These results support efforts to compare findings from depressed patients in China and Western countries.

A longitudinal twin study of cluster A personality disorders

BACKGROUND

While cluster A personality disorders (PDs) have been shown to be moderately heritable, we know little about the temporal stability of these genetic risk factors.

METHOD

Paranoid PD (PPD) and schizotypal PD (STPD) were assessed using the Structured Interview for DSM-IV Personality in 2793 young adult twins from the Norwegian Institute of Public Health Twin Panel at wave 1 and 2282 twins on average 10 years later at wave 2. Using the program Mx, we fitted a longitudinal latent factor model using the number of endorsed criteria for PPD and STPD.

RESULTS

The stability over time of the criteria counts for PPD and STPD, estimated as polychoric correlations, were +0.34 and +0.40, respectively. The best-fit longitudinal model included only additive genetic and individual-specific environmental factors with parameter estimates constrained to equality across the two waves. The cross-wave genetic and individual-specific environmental correlations for a latent cluster A factor were estimated to equal +1.00 and +0.13, respectively. The cross-time correlations for genetic and environmental effects specific to the individual PDs were estimated at +1.00 and +0.16-0.20, respectively. We found that 68% and 71% of the temporal stability of PPD and STPD derived, respectively, from the effect of genetic factors.

CONCLUSION

Shared genetic risk factors for two of the cluster A PDs are highly stable in adults over a 10-year period while environmental risk factors are relatively transient. Over two-thirds of the long-term stability of the common cluster A PD liability can be attributed to genetic influences.

Clarifying the causal relationship in women between childhood sexual abuse and lifetime major depression

BACKGROUND

Childhood sexual abuse (CSA) is strongly associated with risk for major depression (MD) but the degree to which this association is causal remains uncertain.

METHOD

We applied structural equation modeling using the Mplus program to 1493 longitudinally assessed female twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders.

RESULTS

Our model included (i) retrospective self- and co-twin reports on CSA, (ii) major potentially confounding covariates, (iii) assessment of lifetime history of MD at two separate interviews, and (iv) mood-congruent recall (implemented by allowing current depressive symptoms to predict reporting of CSA). In a model with only measurement error, CSA explained 9.6% of MD. Including four key covariates reduced the variance explained to 5.3%, with the largest effects found for parental loss and low parental warmth. Adding the effect of mood-congruent recall to a final well-fitting model reduced the percentage of variance explained in lifetime MD (LTMD) by CSA to 4.4%. In this model, current depressive symptoms significantly predicted recall of CSA.

CONCLUSIONS

In a model correcting for measurement error, confounding and the impact of mood-congruent recall, CSA remains substantially associated with the risk for LTMD in women. These findings strongly suggest, but do not prove, that this association is causal, and are consistent with previous results in this sample using a co-twin control design, but also indicate that more than half of the uncorrected CSA-MD association is probably not causal. Traumatic life experiences contribute substantially to the risk for LTMD.

Evidence for multiple genetic factors underlying the DSM-IV criteria for alcohol dependence

To determine the number of genetic factors underlying the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for alcohol dependence (AD), we conducted structural equation twin modeling for seven AD criteria, plus two summary screening questions, in 7133 personally interviewed male and female twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, who reported lifetime alcohol consumption. The best-fit twin model required three genetic and two unique environmental common factors, and criterion-specific unique environmental factors. The first genetic factor was defined by high loadings for the probe question about quantity and frequency of alcohol consumption, and tolerance criterion. The second genetic factor loaded strongly on the probe question about self-recognition of alcohol-related problems and AD criteria for loss of control, desire to quit, preoccupation and activities given up. The third genetic factor had high loadings for withdrawal and continued use despite the problems criteria. Genetic factor scores derived from these three factors differentially predicted patterns of comorbidity, educational status and other historical/clinical features of AD. The DSM-IV syndrome of AD does not reflect a single dimension of genetic liability, rather, these criteria reflect three underlying dimensions that index risk for: (i) tolerance and heavy use; (ii) loss of control with alcohol associated social dysfunction and (iii) withdrawal and continued use despite problems. While tentative and in need of replication, these results, consistent with the rodent literature, were validated by examining predictions of the genetic factor scores and have implications for gene-finding efforts in AD.

The pathoplasticity of dysphoric episodes: differential impact of stressful life events on the pattern of depressive symptom inter-correlations

BACKGROUND

Previous research has shown that stressful life events (SLEs) influence the pattern of individual depressive symptoms. However, we do not know how these differences arise. Two theories about the nature of psychiatric disorders have different predictions about the source of these differences: (1) SLEs influence depressive symptoms and correlations between them indirectly, via an underlying acute liability to develop a dysphoric episode (DE; common cause hypothesis); and (2) SLEs influence depressive symptoms and correlations between them directly (network hypothesis). The present study investigates the predictions of these two theories.

METHOD

We divided a population-based sample of 2096 Caucasian twins (49.9% female) who reported at least two aggregated depressive symptoms in the last year into four groups, based on the SLE they reported causing their symptoms. For these groups, we calculated tetrachoric correlations between the 14 disaggregated depressive symptoms and, subsequently, tested whether the resulting correlation patterns were significantly different and if those differences could be explained by underlying differences in a single acute liability to develop a DE.

RESULTS

The four SLE groups had markedly different correlation patterns between the depressive symptoms. These differences were significant and could not be explained by underlying differences in the acute liability to develop a DE.

CONCLUSIONS

Our results are not compatible with the common cause perspective but are consistent with the predictions of the network hypothesis. We elaborate on the implications of a conceptual shift to the network perspective for our diagnostic and philosophical approach to the concept of what constitutes a psychiatric disorder.

Binge eating disorder: a symptom-level investigation of genetic and environmental influences on liability

BACKGROUND

Recent behavioral genetic studies have emphasized the importance of investigating eating disorders at the level of individual symptoms, rather than as overall diagnoses. We examined the heritability of binge eating disorder (BED) using an item-factor analytic approach, which estimates contributions of additive genetic (A), common environmental (C), and unique environmental (E) influences on liability to BED as well as individual symptoms.

METHOD

Participants were 614 monozygotic and 410 dizygotic same-sex female twins from the Mid-Atlantic Twin Registry who completed a self-report measure of BED symptoms based upon DSM-IV criteria. Genetic and environmental contributions to BED liability were assessed at the diagnostic and symptom levels, using an item-factor approach.

RESULTS

Liability to BED was moderately heritable; 45% of the variance was due to A, with smaller proportions due to C (13%), and E (42%). Additive genetic effects accounted for 29-43% of the variance in individual items, while only 8-14% was due to C.

CONCLUSIONS

Results highlight the relevance of examining eating disorders at the symptom level, rather than focusing on aggregate diagnoses.

The DSM-IV definition of severity of major depression: inter-relationship and validity

BACKGROUND

Severity is an important characteristic of major depression (MD) and an 'episode specifier' in DSM-IV classifying depressive episodes as 'mild', 'moderate' or 'severe'. These severity subtypes rely on three different measures of severity: number of criteria symptoms, severity of the symptoms and degree of functional disability. No prior empirical study has evaluated the coherence and validity of the DSM-IV definition of severity of MD.

METHOD

In a sample of 1015 (518 males, 497 females) Caucasian twins from a population-based registry who met criteria for MD in the year prior to interview, factor analysis and logistic regression were conducted to examine the inter-relationships of the three severity measures and their associations with a wide range of potential validators including demographic factors, risk for future episodes, risk of MD in the co-twin, characteristics of the depressive episode, the pattern of co-morbidity, and personality traits.

RESULTS

Correlations between the three severity measures were significant but moderate. Factor analysis indicated the existence of a general severity factor, but the factor was not highly coherent. The three severity measures showed differential predictive ability for most of the validators.

CONCLUSIONS

Severity of MD as defined by the DSM-IV is a multifaceted and heterogeneous construct. The three proposed severity measures reflect partly overlapping but partly independent domains with differential validity as assessed by a wide range of clinical characteristics. Clinicians should probably use a combination of severity measures as proposed in DSM-IV rather than privileging one.

A twin study of specific bulimia nervosa symptoms

BACKGROUND

Twin studies have suggested that additive genetic factors significantly contribute to liability to bulimia nervosa (BN). However, the diagnostic criteria for BN remain controversial. In this study, an item-factor model was used to examine the BN diagnostic criteria and the genetic and environmental contributions to BN in a population-based twin sample. The validity of the equal environment assumption (EEA) for BN was also tested.

METHOD

Participants were 1024 female twins (MZ n=614, DZ n=410) from the population-based Mid-Atlantic Twin Registry. BN was assessed using symptom-level (self-report) items consistent with DSM-IV and ICD-10 diagnostic criteria. Items assessing BN were included in an item-factor model. The EEA was measured by items assessing similarity of childhood and adolescent environment, which have demonstrated construct validity. Scores on the EEA factor were used to specify the degree to which twins shared environmental experiences in this model.

RESULTS

The EEA was not violated for BN. Modeling results indicated that the majority of the variance in BN was due to additive genetic factors. There was substantial variability in additive genetic and environmental contributions to specific BN symptoms. Most notably, vomiting was very strongly influenced by additive genetic factors, while other symptoms were much less heritable, including the influence of weight on self-evaluation. These results highlight the importance of assessing eating disorders at the symptom level.

CONCLUSIONS

Refinement of eating disorder phenotypes could ultimately lead to improvements in treatment and targeted prevention, by clarifying sources of variation for specific components of symptomatology.

A psychometric evaluation of the DSM-IV borderline personality disorder criteria: age and sex moderation of criterion functioning

BACKGROUND

Despite its importance as a paradigmatic personality disorder, little is known about the measurement invariance of the DSM-IV borderline personality disorder (BPD) criteria; that is, whether the criteria assess the disorder equivalently across different groups.

METHOD

BPD criteria were evaluated at interview in 2794 young adult Norwegian twins. Analyses, based on item-response modeling, were conducted to test for differential age and sex moderation of the individual BPD criteria characteristics given factor-level covariate effects.

RESULTS

Confirmatory factor analytic results supported a unidimensional structure for the nine BPD criteria. Compared to males, females had a higher BPD factor mean, larger factor variance and there was a significant age by sex interaction on the factor mean. Strong differential sex and age by sex interaction effects were found for the 'impulsivity' criterion factor loading and threshold. Impulsivity related to the BPD factor poorly in young females but improved significantly in older females. Males reported more impulsivity compared to females and this difference increased with age. The 'affective instability' threshold was also moderated, with males reporting less than expected.

CONCLUSIONS

The results suggest the DSM-IV BPD 'impulsivity' and 'affective instability' criteria function differentially with respect to age and sex, with impulsivity being especially problematic. If verified, these findings have important implications for the interpretation of prior research with these criteria. These non-invariant age and sex effects may be identifying criteria-level expression features relevant to BPD nosology and etiology. Criterion functioning assessed using modern psychometric methods should be considered in the development of DSM-V.

Does the level of family dysfunction moderate the impact of genetic factors on the personality trait of neuroticism?

BACKGROUND

While the family environment can directly influence later risk for psychopathology, dysfunction in the family of origin may also moderate the impact of genetic factors on liability for psychiatric disorders. Can a similar pattern be seen for the personality trait of Neuroticism (N)-which is a risk factor for many psychiatric conditions?

METHOD

Our sample of 957 complete female-female twin pairs from a population-based register had measures of self-reported N and multiple reporters (twin, co-twin, mother, father) for family dysfunction (FD). Statistical analysis was conducted by traditional regression analysis and a moderator structural equation twin model operationalized in the computer program Mx.

RESULTS

Dividing the sample into quartiles based on increasing levels of FD, the mean of N increased substantially while correlations of N in monozygotic (MZ) and dizygotic (DZ) twins were relatively constant. Regression analyses did not suggest greater twin resemblance for N with increasing levels of FD. The best-fit structural equation model was the standard un-moderated model in which the proportion of variance in N due to genetic (39%) and unique environmental effects (61%) remained constant across values of FD.

CONCLUSIONS

Although a false-negative result due to limited power cannot be excluded, these analyses do not support the hypothesis that FD moderates the impact of genetic factors on levels of N.

Cannabis use in the last year in a US national sample of twin and sibling pairs

BACKGROUND

Three prior population-based twin studies, none of which was nationally representative, suggested that both genetic and familial-environmental factors contribute to family resemblance for lifetime cannabis use. We seek to replicate these results in a US national probability sample of twin and sibling pairs examining only last year cannabis use.

METHODS

Cannabis use in the last year was assessed by self-report questionnaire. Biometrical twin analyses were performed.

RESULTS

Twin and sibling resemblance for last-year cannabis use was substantial, and much higher in monozygotic pairs than in dizygotic and sibling pairs, where levels of resemblance were similar. Modeling suggested that sibling resemblance was due to genetic factors--with a heritability of at least 60% and probably family environmental factors. No evidence was found that cannabis use was influenced by a special twin environment.

CONCLUSIONS

Consistent with prior studies, use of cannabis is substantially influenced by genetic factors but family-environment is also possibly of importance.

Pregnancy and perinatal complications associated with risks for common psychiatric disorders in a population-based sample of female twins

The association between pregnancy and perinatal complications (PPCs) and risks for adult psychiatric disorders other than psychoses has received relatively limited attention. In this study, we aim to characterize the associations between PPCs and risks for anxiety, affective, substance use, and eating disorders in a population-based sample of twins. Personal interviews were conducted with 1,806 female twin subjects to assess their lifetime history of alcoholism, anorexia nervosa, bulimia nervosa, generalized anxiety disorder, major depression, panic disorder, simple phobias, and social phobias. PPCs were retrospectively assessed at personal interview with the subject's parents. The associations between PPCs and risks for psychiatric disorders are characterized using logistic regression. In this sample of twins, gestational age is associated with a significantly increased risk for anorexia nervosa and pregnancy complications are associated with a significantly increased risk for both anorexia nervosa and bulimia nervosa. Pregnancy and perinatal complications may be associated with an increased risk for eating disorders in women.

Time, memory and the heritability of major depression

OBJECTIVE

Although family, twin and adoption studies have suggested that lifetime major depression (MD) is a heritable condition, nearly all these studies have relied for the diagnosis on long-term human memory, which is fallible and potentially biased. Could the estimates of heritability of MD be biased by the well-demonstrated genetic influences on memory?

METHODS

Both members of 858 female-female twin pairs from a population-based registry were personally interviewed at least three times over 9 years. The interview assessed a history of depressive onsets and recoveries in the last year to the nearest month. We examine heritability of MD using four recall intervals: last year, last 6 months, last 3 months and current month.

RESULTS

Examining the occurrence of one or more depressive episodes across all three interviews, heritabilities of MD (95% CI) for the four time periods were: 0.41 (0.27-0.54), 0.41 (0.26-0.55), 0.35 (0.16-0.52) and 0.34 (0.11-0.55). These heritability estimates did not differ significantly from one another. A similar pattern was found if heritability was assessed for the number of interviews in which criteria for MD were met.

CONCLUSION

Modelling results suggest that the heritability of MD was not influenced by the duration of the required recall. Genetic influences on human recall do not appear to contribute substantially to estimated heritability of MD.

Short-term fluctuations in elderly people's sensorimotor functioning predict text and spatial memory performance: The Macarthur Successful Aging Studies

BACKGROUND

While age-related increases of between-person variability in a variety of cognitive measures are commonly reported in cross-sectional studies, the nature of short-term intraindividual fluctuation in elderly people's performance is relatively unexplored.

OBJECTIVE

The goal of the present study is to examine short-term fluctuations in elderly people's sensorimotor functioning and their relations to individual differences in verbal and spatial memory.

METHODS

Fluctuations in old adults' (mean = 75.71 years, SD = 6.93 years) sensorimotor performance were investigated by biweekly measurements spanning approximately 7 months. Sensorimotor performance was measured by three walking tasks, including the duration and the number of steps taken to walk a 360-degree circle and to walk 10 feet both at normal and fast pace. Performances of verbal and spatial memory were assessed by weekly measurements of digit memory span, memory for short text and spatial recognition.

RESULTS

The magnitude of intraindividual fluctuation in most sensorimotor and memory tasks examined was at least half as great as the level of individual differences across persons. In addition, intraindividual fluctuation in sensorimotor performance is a relatively stable individual attribute, which correlates positively with age and negatively with the levels of sensorimotor, text and spatial memory performance. Although a substantial amount of individual differences in intraindividual fluctuation was shared with mean performance level, variance component and hierarchical regression analyses showed that intraindividual fluctuation in walking steps added significant independent contribution over and above that given by level of performance in predicting text and spatial memory.

CONCLUSION

Taking these results together, we suggest that intraindividual fluctuations in elderly people's performance should not be ignored or simply treated as measurement error; rather, they are potentially important empirical variables for understanding sensory and cognitive aging and the nature of intraindividual response variations in general.

Sex-specific genetic influences on the comorbidity of alcoholism and major depression in a population-based sample of US twins

BACKGROUND

Alcoholism and depression frequently co-occur, but the origins of this comorbidity remain uncertain. Most previous family, twin, and adoption studies of these disorders have used cases ascertained through treatment settings, who may differ from cases in epidemiological samples. We studied the importance of genetic influences on risk for lifetime comorbidity of major depression and alcoholism by means of a population-based twin sample.

METHODS

Lifetime major depression (MD), alcohol abuse, and alcohol dependence were assessed by structured interview for both members of 3755 twin pairs from the Mid-Atlantic Twin Registry. Pair resemblance was analyzed by means of structural equation models.

RESULTS

Individuals with MD were at significantly increased risk for alcohol dependence and for a combined diagnosis of alcohol abuse and/or dependence. History of MD in a twin significantly increased the risk of cotwin alcohol dependence and alcohol abuse and/or dependence among identical male pairs and for alcohol abuse and/or dependence in identical female pairs, but not among male or female fraternal pairs. Results of structural modeling indicate that comorbidity occurs because the genetic and specific environmental sources of liability to MD overlap with those underlying alcohol dependence and alcohol abuse and/or dependence. This overlap was significant only within sex, not across sexes.

CONCLUSIONS

In this population-based twin sample, the familial transmission of MD and alcohol dependence was largely disorder specific. Comorbidity appears to be due to sex-specific genetic and environmental risk factors. The factors underlying depression in women do not appear to arise from the same factors underlying alcoholism in men.

Similarity in saliva cortisol measures in monozygotic twins and the influence of past major depression

BACKGROUND

Some studies suggest that cortisol may be under genetic control. The aims of our study were to investigate the familial resemblance in morning and evening cortisol secretion as assessed by saliva cortisol and to assess the influence of history of major depression.

METHODS

Women for this investigation were selected from an ongoing study in female-female twin pairs ascertained from the Virginia Twin Registry. Telephone screening assured that current inclusion/exclusion criteria were met. Subjects were asked to collect AM samples within 45 min after awakening, and evening samples immediately before bedtime for 14 days.

RESULTS

There was a high degree of correlation across weeks in both the AM and PM cortisol values, indicating significant stability across individuals. There was significant correlation between AM and PM cortisol in monozygotic twins. In twins with a history of major depression (n = 30), compared with the twins without past major depression (n = 28), there was a trend towards higher cortisol (p = .056).

CONCLUSIONS

These results suggest that around 40-45% of the total variance in salivary cortisol is shared by monozygotic twins. Although the increase in baseline cortisol in twins with a history of major depression is only significant at the trend level, the effect size is comparable to an "in episode" depressed population.

Sex differences in the sources of genetic liability to alcohol abuse and dependence in a population-based sample of U.S. twins

BACKGROUND

There are substantial sex differences in all levels of alcohol involvement among U.S. adults. The goal of this study was to test whether the magnitude and sources of genetic and environmental influences on liability for alcohol abuse and dependence differ for men and women.

METHODS

Structured personal interviews were used to assess DSM-III-R- and DSM-IV-defined alcohol abuse and dependence among 5091 male and 4168 female twins (including 1546 identical, 1128 same-sex fraternal, and 1423 opposite-sex pairs) born in Virginia between 1934 and 1974. Twin correlations were analyzed using structural equation modeling.

RESULTS

The magnitude of twin-pair resemblance was similar across several definitions of alcoholism and was substantially higher among identical than fraternal pairs. The proportion of population variation in liability attributed to genetic factors was substantial among both women (55-66%) and men (51-56%), and we found little evidence of a role of environmental factors shared by family members. In all definitions studied, we could reject a model that the genetic sources of liability in the two sexes overlap completely.

CONCLUSION

In this first population-based study of alcoholism among male and female twins from the U.S., we found that genetic factors play a major role in the development of alcoholism in both sexes, that the magnitudes of genetic influence were equally high for men and women, and that the genetic sources of vulnerability are partially, but not completely, overlapping in men and women.