Overlapping genetic and environmental influences among men's alcohol consumption and problems, romantic quality and social support

BACKGROUND

Alcohol consumption and problems are associated with interpersonal difficulties. We used a twin design to assess in men the degree to which genetic or environmental influences contributed to the covariance between alcohol consumption and problems, romantic quality and social support.

METHOD

The sample included adult male-male twin pairs (697 monozygotic and 487 dizygotic) for whom there were interview-based data on: alcohol consumption (average monthly alcohol consumption in the past year); alcohol problems (lifetime alcohol dependence symptoms); romantic conflict and warmth; friend problems and support; and relative problems and support.

RESULTS

Key findings were that genetic and unique environmental factors contributed to the covariance between alcohol consumption and romantic conflict; genetic factors contributed to the covariance between alcohol problems and romantic conflict; and common and unique environmental factors contributed to the covariance between alcohol problems and friend problems.

CONCLUSIONS

Recognizing and addressing the overlapping genetic and environmental influences that alcohol consumption and problems share with romantic quality and other indicators of social support may have implications for substance use prevention and intervention efforts.

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.

Accounting for the association between childhood maltreatment and alcohol-use disorders in males: a twin study

BACKGROUND

An association between childhood maltreatment and subsequent alcohol abuse and/or dependence (AAD) has been found in multiple studies of females. Less is known about the association between childhood maltreatment and AAD among males, and the mechanisms that underlie this association in either gender. One explanation is that childhood maltreatment increases risk for AAD. An alternative explanation is that the same genetic or environmental factors that increase a child's risk for being maltreated also contribute to risk for AAD in adulthood.

METHOD

Lifetime diagnosis of AAD was assessed using structured clinical interviews in a sample of 3527 male participants aged 19-56 years from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. The sources of childhood maltreatment-AAD association were estimated using both a matched case-control analysis of twin pairs discordant for childhood maltreatment and bivariate twin modeling.

RESULTS

Approximately 9% of participants reported childhood maltreatment, defined as serious neglect, molestation, or physical abuse occurring before the age of 15 years. Those who experienced childhood maltreatment were 1.74 times as likely to meet AAD criteria compared with males who did not experience childhood maltreatment. The childhood maltreatment-AAD association largely reflected environmental factors in common to members of twin pairs. Additional exploratory analyses provided evidence that AAD risk associated with childhood maltreatment was significantly attenuated after adjusting for measured family-level risk factors.

CONCLUSIONS

Males who experienced childhood maltreatment had an increased risk for AAD. Our results suggest that the childhood maltreatment-AAD association is attributable to broader environmental adversity shared between twins.

The Norwegian Institute of Public Health twin study of mental health: examining recruitment and attrition bias

All Norwegian twin pairs born 1967-1974 and still living in Norway in 1992 were invited to a health questionnaire study (Q1). 2,570 pairs (65%) participated. These cohorts and the twin cohorts born 1967-1979 were invited to a new questionnaire study (Q2) in 1998. This time 3,334 pairs (53%) participated. Almost all pairs having participated in the 1998 study were invited to an interview study of mental health (MHS), taking place 1999-2004. 1,391 complete pairs (44%) participated. The questionnaire studies included extensive data on somatic health with fewer items on mental health and demography. Health-related and demographic information available from the Medical Birth Registry on all invited twins was applied to predict participation to the first study. A few registry variables indicating poor health predicted nonparticipation in Q1. Health information and demography from Q1 were tested as predictors of participation in the follow-up study (Q2). Monozygosity, female sex, being unmarried, having no children, and high education predicted participation, whereas few indicators of poor mental and somatic health and unhealthy lifestyle moderately predicted nonparticipation in Q2. No health indicators reported in Q2 predicted further participation. Standard genetic twin analyses of indicators of various mental disorders from Q2, validated by diagnostic data from the MHS, did not indicate differences in genetic/environmental covariance structures between participants and nonparticipants in MHS. In general the results show a moderate selection towards good mental and somatic health. Attrition from Q2 to the MHS does not appear to affect twin analyses of mental health related variables.

Alcohol dependence is associated with the ZNF699 gene, a human locus related to Drosophila hangover, in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD) sample

Because tolerance is an important aspect of alcohol dependence (AD) in humans, recent evidence showing that the Drosophila gene hang is critically involved in the development of alcohol tolerance in the fly suggests that variation in related human loci might be important in the etiology of alcohol-related disorders. The orthology of hang in mammals is complex, but a number of human gene products (including ZNF699) with similar levels of amino-acid identity (18-26%) and similarity (30-41%), are consistently identified as the best matches with the translated hang sequence. We tested for association between the dichotomous clinical phenotype of alcohol dependence and seven single nucleotide polymorphisms (SNPs) in ZNF699 in our sample of 565 genetically independent cases and 496 siblings diagnosed with AD, and 609 controls. In analyses of genetically independent cases and controls, four of the seven single markers show strong evidence for association with AD (0.00003<Fisher's exact P<0.001), and the most significant single marker, rs7254880, tags an associated haplotype with frequency 0.071 in cases compared to 0.034 in controls (chi2 15.563, P<0.00008, 5000 permutation P<0.001, OR 2.17); inclusion of affected siblings gives similar results. Expression analyses conducted in independent postmortem brain samples show that expression of ZNF699 mRNA is significantly reduced in the dorsolateral prefrontal cortex of individuals carrying this haplotype compared with other observed haplotype combinations.

Genomewide linkage study in the Irish affected sib pair study of alcohol dependence: evidence for a susceptibility region for symptoms of alcohol dependence on chromosome 4

Alcoholism is a relatively common, chronic, disabling and often treatment-resistant disorder. Evidence from twin and adoption studies indicates a substantial genetic influence, with heritability estimates of 50-60%. We conducted a genome scan in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD). Most probands were ascertained through alcoholism treatment settings and were severely affected. Probands, affected siblings and parents were evaluated by structured interview. A 4 cM genome scan was conducted using 474 families of which most (96%) were comprised by affected sib pairs. Nonparametric and quantitative linkage analyses were conducted using DSM-IV alcohol dependence (AD) and number of DSM-IV AD symptoms (ADSX). Quantitative results indicate strong linkage for number of AD criteria to a broad region of chromosome 4, ranging from 4q22 to 4q32 (peak multipoint LOD=4.59, P=2.1 x 10(-6), at D4S1611). Follow-up analyses suggest that the linkage may be due to variation in the symptoms of tolerance and out of control drinking. There was evidence of weak linkage (LODs of 1.0-2.0) to several other regions, including 1q44, 13q31, and 22q11 for AD along with 2q37, 9q21, 9q34 and 18p11 for ADSX. The location of the chromosome 4 peak is consistent with results from prior linkage studies and includes the alcohol dehydrogenase gene cluster. The results of this study suggest the importance of genetic variation in chromosome 4 in the etiology and severity of alcoholism in Caucasian populations.

Illicit drug use and abuse/dependence: modeling of two-stage variables using the CCC approach

Drug use and abuse/dependence are stages of a complex drug habit. Most genetically informative models that are fit to twin data examine drug use and abuse/dependence independent of each other. This poses an interesting question: for a multistage process, how can we partition the factors influencing each stage specifically from the factors that are common to both stages? We used a causal-common-contingent (CCC) model to partition the common and specific influences on drug use and abuse/dependence. Data on use and abuse/dependence of cannabis, cocaine, sedatives, stimulants and any illicit drug was obtained from male and female twin pairs. CCC models were tested individually for each sex and in a sex-equal model. Our results suggest that there is evidence for additive genetic, shared environmental and unique environmental influences that are common to illicit drug use and abuse/dependence. Furthermore, we found substantial evidence for factors that were specific to abuse/dependence. Finally, sexes could be equated for all illicit drugs. The findings of this study emphasize the need for models that can partition the sources of individual differences into common and stage-specific influences.

A twin study of personality and illicit drug use and abuse/dependence

Although personality measures such as neuroticism (N), extraversion (E) and novelty-seeking (NS) are associated with the use and abuse/dependence of illicit drugs, little is known about the degree to which these associations are due to genetic or environmental factors. The goal of this analysis was to estimate the extent of genetic and environmental overlap between three dimensions of personality (N, E and NS) and illicit psychoactive substance use and abuse/dependence. Using data from adult male and female twins from the Mid-Atlantic Twin Registry, we used the structural equation modeling package Mx to perform bivariate Cholesky decompositions for personality measures of N, E and NS, individually with cannabis, cocaine, sedatives, stimulants and hallucinogens. This was done separately for use and for a polychotomous diagnosis of abuse and/or dependence. Sex differences were tested. The phenotypic relationship between personality and use and abuse/dependence of illicit drugs were moderate and most of the covariance was explained by genetic factors. Sexes could be equated for N and E but not for NS. For NS, use and abuse/dependence of illicit drugs showed greater phenotypic and genetic overlap in males than females. Of the personality measures, NS and illicit drug use and abuse/dependence were most closely related. NS was most closely related to cannabis use while N showed significant genetic overlap with sedative use. NS in males appears to be a good indicator of risk for cannabis use. This result may be useful for candidate gene studies.

The prediction of thoughts of death or self-harm in a population-based sample of female twins

BACKGROUND

Although suicide is a leading cause of death, few studies have attempted to predict suicidal ideation prospectively using epidemiological samples or multivariate methods.

METHOD

Discrete-time event history analysis was used to model the onset of thoughts of death or self-harm (TD/SH) in a population-based sample of female twins (N=2164) using variables from the demographic, psychopathological, childhood adversity, personality and life event domains. Univariate, multivariate-within domain and multivariate-across domain regression analyses were performed.

RESULTS

Most variables predicted TD/SH in the univariate analyses. However, the only variables to predict TD/SH independently were obsessive symptoms, childhood sexual abuse, rural residence, unemployment, older age, lifetime history of cocaine misuse and low levels of education, personal religious devotion and altruism, as well as divorce/separation, loss of confidant, assault, job loss and financial problems in the previous month. This final model explained 16% of the variance in TD/SH. Lifetime histories of major depression, panic disorder and alcohol misuse had no significant independent effect.

CONCLUSIONS

Many variables, from all five domains of risk factors, are associated with the risk of TD/SH, but many of these effects may be mediated by other risk factors. Proximal life events and psychopathology may have more independent effects than other domains. The overall ability of these risk factors to predict TD/SH is modest. We cannot rule out that differences between these analyses and previous reports were due to our use of TD/SH as the dependent variable instead of thoughts of committing suicide per se.

The effects of anxiety, substance use and conduct disorders on risk of major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is highly co-morbid with other Axis I disorders, which commonly precede its onset. We sought to determine the level and periods of risk for MDD posed by prior or co-occurring psychiatric disorders.

METHOD

Using retrospective data from a longitudinal, population-based sample of 2926 male and 1929 female adult twin subjects, we predicted the hazard rates for MDD from a Cox proportional hazards model with same-year or prior onsets of co-morbid Axis I disorders as time-dependent covariates.

RESULTS

All axis I disorders studied (generalized anxiety disorder, panic disorder, phobia, alcohol dependence, psychoactive substance use disorders and conduct disorder) significantly predicted increased risk for developing MDD. The highest hazard rates occurred for MDD onsets that co-occurred with those of the co-morbid disorder. However, the risk for onset of MDD subsequent to that of prior disorders is also significantly increased and remains relatively unchanged over time. Although the risk for onset of MDD is significantly higher in women than men, this was not explained by gender differences in prior disorder prevalence or increased sensitivity in women to the effects of prior disorders on risk for depression.

CONCLUSIONS

Prior psychiatric disorders are significant risk factors for the development of MDD, independent of the length of the intervening period between the onset of the first disorder and that of MDD.

Personality and the experience of environmental adversity

BACKGROUND

While psychiatric epidemiology often focuses on the causal relationship between environmental adversity and the individual (e.g. environment to person), individuals probably make important contributions to the quality of their environments (person to environment).

METHOD

In a population based sample of > 7000 male and female adult twins, we examined the relationship between the personality trait of neuroticism (N) and the occurrence of stressful life events (SLEs) and the quality of interpersonal relationships (IPR). We compared the magnitude of the prediction of twin 1's self-reported SLEs and IPR from: (i) twin 1's self-reported N; (ii) twin 2's report of twin 1's N; and (iii) twin 2's report of twin 2's N in monozygotic pairs.

RESULTS

In our entire sample, self-report N significantly predicted the occurrence of most SLEs and all dimensions of IPR. Using the co-twin's report of N produced associations that were of the same magnitude for SLEs and modestly weaker for IPR. In monozygotic pairs, the level of N in one twin predicted SLEs and IPR in the co-twin at levels similar to those found for the co-twin's report of N. Repeating these analyses with a prospective subsample produced similar results.

CONCLUSION

An individual's personality in adulthood plays a significant role in influencing exposure to some forms of environmental adversity and this association is not the result of reporting bias. Furthermore, this relationship is largely mediated by a common set of familial factors that predispose both to a 'difficult' temperament and to environmental adversity. Developmental models of psychiatric illness should adopt an interactionist view of individuals and their environment (person and environment).

Interpersonal dependence and major depression: aetiological inter-relationship and gender differences

BACKGROUND

Although prior research has demonstrated a strong association between interpersonal dependency (IPD) levels and risk for major depression (MD), the possible aetiological explanations of this association as well as any gender differences in the IPD-MD relationship need further clarification.

METHOD

Population-based twin samples (N = 7174) were interviewed in multiple waves to assess IPD and MD as part of a larger twin study. IPD levels were assessed using the Interpersonal Dependency Inventory while MD diagnoses were derived from the SCID. Cox proportional hazard models and multiple regression techniques were utilized.

RESULTS

IPD was strongly associated with a risk for lifetime MD. Pre-morbid IPD scores were predictive of future onsets of MD while experiencing a MD episode was also associated with a significant rise in IPD levels. While females had higher IPD scores, IPD scores were more significantly associated with risk for lifetime MD in males. Controlling for the level of IPD substantially reduced the observed association between gender and risk for MD.

CONCLUSION

The strong association observed between IPD and risk for MD results largely from IPD being a risk factor for MD, but state effects of MD on IPD also contribute. IPD scores in males were more predictive of lifetime MD than for females. The higher levels of IPD in women than in men may contribute meaningfully to the sex differences in risk for MD.

Fatigue in a community sample of twins

BACKGROUND

Fatigue is a complex symptom associated with many physiological, psychological and pathological processes. Its correlates and typology remain inadequately understood.

METHOD

These data were from two large, longitudinal twin studies. Trained interviewers enquired as to the presence of a > or = 5 day period in the previous year of fatigue or tiredness that interfered with daily activities. A range of potential correlates was assessed in a structured interview: demography; health beliefs; the presence of nine physical disorders; mood, anxiety and addictive disorders; neuroticism and extraversion; recollections of parental rearing; and nine stressful life events. Statistical analyses included logistic regression, CART, MARS, latent class analysis and univariate twin modelling.

RESULTS

Data were available for interfering fatigue (IF) on 7740 individual twins (prevalence 9.9% in the previous year). IF was significantly associated with 42 of 52 correlates (most strongly with major depression, generalized anxiety disorder, reported major health problems and neuroticism). Multivariate analyses demonstrated that IF is a highly complex construct with different sets of correlates in its subtypes. There were two broad clusters of correlates of IF: (a) major depression, generalized anxiety disorder and neuroticism; and (b) beliefs of ill health coexisting with alcoholism and stressful life events. Twin analyses were consistent with aetiological heterogeneity--genetic effects may be particularly important in women and shared environmental effects in men.

CONCLUSIONS

IF is a complex and common human symptom that is highly heterogeneous. More precise understanding of the determinants of IF may lead to a fuller understanding of more extreme conditions like chronic fatigue syndrome.

A twin study of sex differences in social support

BACKGROUND

Social support may reduce the risk of psychiatric illness. Though perceived as an environmental measure, genetic factors may influence levels of social support. A relationship between social roles and personality with social support suggests possible sex effects on the sources of individual differences in social support.

METHOD

We used the responses of MZ and DZ same and opposite sex twins to 16 questions regarding their social life. Six factors--friend support, relative support, friend problem, relative problem, confidants and social integration were used for structural equation modelling. Factor derived scales were analysed for genetic, shared and unique environmental influences. Quantitative and qualitative gender differences were analysed using the software package Mx.

RESULTS

Except for relative support and confidants, no qualitative sex differences were seen. Genetic and individual specific environmental influences accounted for the variance for friend support, friend problems, relative problems and social integration and no quantitative gender differences were seen. For relative support genetic factors were detected in females but not males, while for confidants, the shared environment was important in females but not males.

CONCLUSIONS

Except for relative support in males, genetic factors influence variation in all dimensions of social support. Shared environmental factors influence relative support and relative problems in both sexes. Sex differences were detected for confidants and relative support.

Childhood parental loss and risk for first-onset of major depression and alcohol dependence: the time-decay of risk and sex differences

BACKGROUND

Whereas a number of studies have suggested that parental loss is associated with increased risk for major depression (MD), much less is known about possible gender differences, diagnostic specificity and the time course of the impact of loss.

METHOD

First-onsets for MD and alcohol dependence (AD) were assessed at personal interviews in 5070 twins from same-sex (SS) and 2118 from opposite-sex (OS) twin pairs ascertained from a population-based registry. Cox Proportional Hazard (PH) and Non-Proportional Hazard (NPH) models, examining first onsets of MD and AD, were used with twins from SS pairs and conditional logistic regression for OS pairs. Parent-child separations prior to age 17 were divided into death and separation from other causes.

RESULTS

The PH assumptions of constant increased risk were rejected for the impact of loss on risk for MD but not for AD. NPH models found significantly increased risk for MD after both death and separation with the risk lasting much longer for separations. For AD, the PH model found significantly increased risk after parental separation but not death. In both SS and OS twin pairs, no sex differences were seen in the impact of parental loss on risk for MD whereas the association between separation and risk for AD was significantly stronger in females than in males.

CONCLUSION

Consistent sex differences in the association with parental loss were seen for AD but not MD. The analysis of the time-course of increased risk after loss suggests three different patterns which may reflect different relationships: parental death and MD (return to baseline within approximately 12 years), separation and MD (return to baseline within approximately 30 years) and separation and AD (no change in risk over time).

The joint analysis of personal interview and family history diagnoses: evidence for validity of diagnosis and increased heritability estimates

BACKGROUND

Psychiatric diagnoses obtained at personal interview are only moderately reliable and depend critically on accurate self-observation. Reports by family members provide additional information but may be biased. It is unclear how best to combine these two sources of diagnostic data.

METHODS

Using complete data on lifetime prevalence for six disorders in approximately 1200 male-male twin pairs from a population based registry, we first applied a standard bivariate twin model--which treats self-diagnoses and informant-diagnoses as separate phenotypes--and then examined a 'multiple-rater' model--which assumes that self-report and co-twin-report are fallible indices of one underlying disease liability. Best-fit models were chosen using Akaike's information criterion.

RESULTS

Standard bivariate analyses indicated that the same genetic factors accounted for variation in self-reported and co-twin-reported diagnoses. The multiple-rater model produced a substantial decrease in variance attributed to individual-specific environment and a proportional increase in heritability of liability for major depression, generalized anxiety disorder, alcohol dependence and adult antisocial behaviour, but not for drug abuse/dependence or regular tobacco use. The best-fit model consistently included either a 'bias' or a 'correlated error' path. No evidence for family environmental risk factors was found for any disorder.

CONCLUSION

The genetic factors that influence self-report psychiatric illness also influence psychiatric illness as described by relatives. For many psychiatric disorders, incorporation of self-report and family history data in a single model may reduce measurement error and increase estimates of heritability. However, account must be taken of the fact that family history reports are systematically biased. While promising, these results are preliminary and require replication.

Neuroticism, major depression and gender: a population-based twin study

BACKGROUND

A portion of the genetic risk factors for the personality trait neuroticism (N) may also increase risk for major depression (MD). Females have both higher levels of N and higher rates of MD than males, suggesting that these traits may be more genetically correlated in females.

METHODS

Structured interviews, including a lifetime assessment for MD by DSM-III-R criteria, were administered to 863 male-male MZ (monozygotic), 649 male-male DZ (dizygotic), 506 female-female MZ, 345 female-female DZ, and 1,408 opposite-sex twin pairs. N was assessed using the short-form of the Eysenck Personality Questionnaire. A sex-limited Cholesky model was fitted which allowed us to decompose into additive genetic, common environmental, and individual-specific environmental components two main classes of correlations: within-sex between-variable and between-sex within-variable.

RESULTS

Our best-fitting model contained only additive genetic and individual-specific environmental factors for both N and MD. The within-sex genetic correlations between N and MD were estimated at +0.68 in men and +0.49 in women. This model fitted only slightly better than one in which the N-MD within-sex genetic correlation was constrained to be equal across the sexes, and estimated at +0.55. There may be sex-specific genes influencing both N and MD.

CONCLUSION

Our best-fitting model failed to establish a significant sex difference in the genetic correlation between N and MD. These results, as well as evidence for sex-specific genetic factors for both traits, have implications for the diagnosis, classification, and treatment of the affective disorders, and molecular genetic approaches to the study of these traits.

Sex differences in genetic and environmental risk factors for irrational fears and phobias

BACKGROUND

For irrational fears and their associated phobias, epidemiological studies suggest sex differences in prevalence and twin studies report significant genetic effects. How does sex impact on the familial transmission of liability to fears and phobias?

METHODS

In personal interviews with over 3000 complete pairs (of whom 1058 were opposite-sex dizygotic pairs), ascertained from a population-based registry, we assessed the lifetime prevalence of five phobias and their associated irrational fears analysed using a multiple threshold model. Twin resemblance was assessed by polychoric correlations and biometrical model-fitting incorporating sex-specific effects.

RESULTS

For agoraphobia, situational and blood/injury fear/phobia, the best fit model suggested equal heritability in males and females and genetic correlations between the sexes of less than +0.50. For animal fear/phobias by contrast, the best fit model suggested equal heritability in males and females and a genetic correlation of unity. No evidence was found for an impact of family environment on liability to these fears or phobias. For social phobias, twin resemblance in males was explained by genetic factors and in females by familial-environmental factors.

CONCLUSION

The impact of sex on genetic risk may differ meaningfully across phobia subtypes. Sex-specific genetic risk factors may exist for agoraphobia, social, situational and blood-injury phobias but not for animal fear/phobia. These results should be interpreted in the context of the limited power of twin studies, even with large sample sizes, to resolve sex-specific genetic effects.

Features of childhood sexual abuse and the development of psychiatric and substance use disorders

BACKGROUND

Childhood sexual abuse (CSA) is associated with an increased risk of subsequent psychiatric disorders.

AIMS

To explore the risk associated with features of CSA and examine whether specific associations exist between particular profiles of CSA and the development of specific syndromes.

METHOD

In a population-based sample of adult female twins, we used logistic regression to explore the association between features of CSA (reported by the twin and her co-twin) and lifetime major depression, generalised anxiety disorder, bulimia nervosa, panic disorder and alcohol and drug dependence.

RESULTS

In univariate and stepwise multiple regressions, patterns of predictors differed, although not significantly, across diagnoses. Greater risk was associated with attempted or completed intercourse, the use of force or threats, abuse by a relative, and a negative response by someone who was told about the abuse. Similar patterns were observed with co-twin reports.

CONCLUSIONS

Specific features of CSA differentially increase risk of later psychopathology; however, there do not appear to be unique predictive relationships between features of CSA and the emergence of specific psychiatric disorders.

Associations between marital status and alcohol consumption in a longitudinal study of female twins

OBJECTIVE

Prior studies have documented an association between marriage and lower alcohol consumption. Data from a longitudinal study of female twins were used to address whether longitudinal drinking trajectories are more closely related to current marital status or to patterns of marital status over time.

METHOD

Past-year alcohol consumption frequency and quantity were obtained on one to three occasions, over 8 years, from 1,986 women aged 17-61. Latent growth models were applied to study whether trajectories of alcohol consumption are altered at first marriage and differ for women with different patterns of marital status changes.

RESULTS

There was substantial heterogeneity in consumption trajectories, but marital status was associated with a large proportion of the decline in consumption prior to age 30. Significant group differences in consumption trajectory were associated with marital status patterns; women who later divorced drank more than women who stayed married, and divorced women who remarried drank less than divorced women who did not remarry. Among identical twins, consumption patterns were associated with co-twin divorce, suggesting the marital "effect" may be partially due to family-level factors that influence drinking.

CONCLUSIONS

The results are consistent with a decrease in drinking accompanying the transition from being single to first marriage, but the influences of divorce on drinking appear to exist prior to divorce, are not directly associated with current status and may be mediated by familial processes. These results suggest that the influences of marriage on alcohol consumption are complex and cannot be limited to the simple view that marriage causes decreased drinking.

Panic syndromes in a population-based sample of male and female twins

BACKGROUND

The risk for panic disorder (PD) is substantially increased in relatives of probands with PD. Prior literature provides only limited information about the degree to which this increase is due to genetic factors or family environment.

METHODS

In personal interviews with both members of 3194 twin pairs, we assessed the lifetime history of lifetime panic attacks and PD. Twin resemblance was assessed by tetrachoric correlation and single and multiple threshold biometrical model fitting.

RESULTS

As fully syndromal PD, by DSM-III-R criteria, was too rare to analyse usefully we examined four other dichotomous definitions of increasing stringency: panic probe and very broad, broad and intermediate PD. For all four definitions and for the multiple threshold analyses, the best-fit model indicated that twin resemblance was due solely to genetic factors with a moderate heritability (33-43%). For the broad and intermediate dichotomous definitions of PD, however, a model with twin resemblance due to familial-environmental factors fit nearly as well. No gender effects were seen on the genetic risk factors for these PD-like syndromes.

CONCLUSION

Even with large epidemiological samples of twins, studying disorders as uncommon as PD is problematical. Despite these difficulties, our results suggest that: (i) narrowly and broadly defined PD are probably on the same continuum of liability; (ii) twin resemblance for these PD-like syndromes is likely due largely to genetic factors with a moderate level of heritability although a contribution of familial-environmental factors cannot be excluded, and, (iii) the same familial risk factors impact. to a similar degree, on the liability to PD in males and females.

A population-based twin study of generalized anxiety disorder in men and women

This study aimed to a) assess whether genetic or environmental effects are of similar magnitude in the etiology of GAD in men and women, and b) investigate whether familial (genetic or common environmental) risk factors are the same in men and women, or whether there are gender-specific effects. We obtained a lifetime history of DSM-IIII-R GAD, via face-to-face and telephone interviews, from 3100 complete male-male, female-female, and male-female twin pairs, ascertained through a population-based registry. Biometrical twin modeling was utilized to estimate the relative contributions of genetic and environmental factors to liability for GAD, allowing for gender-specific effects. The familial aggregation of GAD in this sample was only modest. In the best-fitting models, the heritability of GAD was the same in men and women, estimated at about 15% to 20%, with no effects of gender-specific genes detected.

Are there sex differences in the reliability of a lifetime history of major depression and its predictors?

BACKGROUND

Although lifetime major depression (LTMD) is assessed with only moderate reliability in community samples, some predictors have emerged for 'reliable' LTMD. Given the large impact of sex on risk for LTMD, it is of interest to know if there are sex differences in the reliability of LTMD and its predictors.

METHODS

A total of 5603 members of male-male and male-female twin pairs from a population-based registry were interviewed twice with a mean inter-interview interval of 19 months. LTMD was assessed on each occasion using DSM-III-R criteria. Univariate and multivariate logistic regression analyses were used, combining forward and back-prediction.

RESULTS

The long-term test-retest reliability of LTMD was moderate (kappa = +0.48) and did not differ significantly between males and females. In a multivariate model, the significant predictors of a stable diagnosis of LTMD, none of which differed across sex, were younger age at onset, older current age, history of treatment, increasing number of symptoms, level of impairment or level of distress, longer duration of episodes, higher current level of depression and the presence during the depressive episode of sad mood, weight loss, hypersomnia or fatigue. Using these variables, it was not possible to predict 'stably diagnosed' LTMD with both high sensitivity and high specificity.

CONCLUSION

In community samples, LTMD is diagnosed with moderate reliability. Although diagnostic stability can be predicted by variables related to severity, distress and treatment-seeking (probably acting to make depressive episodes more 'memorable'), highly accurate prediction of stably diagnosed cases is not possible. Long-term recall is also significantly influenced by current symptoms. Neither the stability of LTMD nor its predictors differ in men and women.

Genetic risk factors for major depression in men and women: similar or different heritabilities and same or partly distinct genes?

BACKGROUND

Although women are at consistently greater risk for major depression (MD) than men, it is unclear whether sex modifies the aetiological impact of genetic factors on MD. Is the heritability of MD different in men and women? Do the same genetic risk factors predispose to MD in the two sexes?

METHODS

We obtained a lifetime history of MD by personal interview on two occasions from 6672 individual twins and 2974 complete twin pairs. Three diagnostic criteria of increasing narrowness were employed: DSM-III-R, DSM-III-R plus impairment and Washington University. To increase power by controlling for unreliability of assessment, we evaluated sex differences on genetic risk for MD using a structural equation measurement model.

RESULTS

Using DSM-III-R criteria, but not the two narrower definitions, heritability of MD was significantly greater in women than in men. In the three diagnostic systems, the genetic correlation in liability to MD in men and women was estimated at between +0.50 and +0.65. These estimates differed significantly from unity for the two broader definitions.

CONCLUSION

Using broad but not narrower definitions of illness, genetic factors play a greater role in the aetiology of MD in women than in men. The genes that influence risk for MD in the two sexes are correlated but are probably not entirely the same. These results raise the possibility that, in linkage and association studies, the impact of some loci on risk for MD will differ in men and women.

Gender differences in the rates of exposure to stressful life events and sensitivity to their depressogenic effects

OBJECTIVE

Women are at greater risk for major depression than men. The authors sought to determine whether the gender difference in prevalence for major depression was due to more frequent exposure to stressful life events and/or greater sensitivity to their depressogenic effects.

METHOD

Male-male, female-female, and male-female twin pairs from a population-based registry were personally interviewed. Each interview assessed the occurrence, to the nearest month, of 18 personal and social network classes of stressful life events and episode onsets of major depression. Standard logistic regression analyses were conducted for the same-sex pairs, and each female twin in the opposite-sex pairs was compared with her male co-twin by using conditional logistic regression.

RESULTS

Women consistently reported higher rates of housing problems, loss of confidant, crises and problems getting along with individuals in their proximal network, and illness of individuals within their distal network. In both the same-sex and opposite-sex samples, men reported higher rates of job loss, legal problems, robbery, and work problems. Consistent sex differences in the depressogenic effect of stressful life events were seen for three event categories: men were more sensitive to the depressogenic effects of divorce or separation and work problems; women were more sensitive to the depressogenic effects of problems getting along with individuals in their proximal network. None of the gender difference in prevalence of major depression could be explained by differing rates of or sensitivities to stressful life events.

CONCLUSIONS

Women reported more interpersonal whereas men reported more legal and work-related stressful life events. Most life event categories influenced the risk for major depression similarly in the two sexes. The results suggest that the greater prevalence of major depression in women versus men is due neither to differences in the rates of reported stressful life events nor to differential sensitivity to their pathogenic effect.

Genetic and environemental factors in conduct problems and adult antisocial behavior among adult female twins

Most twin and adoption studies of conduct problems have demonstrated modest genetic effects but substantial contributions of shared family environment. Conversely, most investigations have shown marked genetic influences but modest contributions of shared family environment in adult antisocial behavior. However, most previous work has focused on male subjects. We obtained retrospective reports of DSM-III-R-defined conduct disorder (CD) and adult antisocial behaviors from a population-based sample of female-female twin pairs. Genetic and environmental contributions to conduct problems and adult antisocial behaviors were examined using polychoric correlation coefficients and univariate structural equation modeling. Statistically significant but modest heritability was observed for conduct problems. A small, statistically nonsignificant contribution of shared family environment to CD behavior was also noted. Adult antisocial symptoms showed modest contributions of both additive genetic and shared family environmental factors. In both childhood and adulthood, the largest influence on antisocial behavior was individual-specific environment. Our findings support the importance of both genetic and environmental factors in antisocial behavior among women as well as the possibility that the relative importance of each set of influences differs by sex in both childhood and adulthood.

The genetic epidemiology of irrational fears and phobias in men

BACKGROUND

Much of our knowledge of the role of genetic factors in the etiology of phobias comes from one population-based sample of female twins. We examined the sources of individual differences in the risks for phobias and their associated irrational fears in male twins.

METHODS

In personal interviews with both members of 1198 male-male twin pairs (707 monozygotic [MZ] and 491 dizygotic [DZ]) ascertained from a population-based registry, we assessed the lifetime history of agoraphobia and social, animal, situational, and blood/injury phobias as well as their associated irrational fears. Twin resemblance was assessed by means of probandwise concordance, odds ratios, tetrachoric correlations, and univariate and multivariate biometrical model fitting.

RESULTS

The suggestive results obtained by analysis of phobias only were supported by analyzing both fears and phobias. All 5 phobia subtypes aggregate within twin-pairs. This aggregation is due largely or solely to genetic factors with heritability of liabilities ranging from 25% to 37%. Multivariate analysis revealed a common genetic factor, genetic factors specific to each subtype, and a common familial-environmental factor.

CONCLUSIONS

In male subjects, genetic risk factors, which are partially common across all subtypes and partially subtype specific, play a moderate role in the etiology of phobias and their associated irrational fears. Family environment probably has an impact on risk for agoraphobia and social phobia. The genetic liability to blood/injury phobias is not distinct from those of the more typical phobias.

Obsessive and compulsive symptoms in a general population sample of female twins

Obsessive-compulsive disorder (OCD) and obsessive-compulsive symptoms (OCS) exhibit a familial pattern of transmission. The different components of these conditions and the extent to which these components are inherited have not been studied well. A sample of 1,054 female twins, including both members of 527 pairs, from the Virginia Twin Registry returned questionnaires that included 20 items from the Padua Inventory of obsessive-compulsiveness. Their responses were used to estimate the heritability of the different factors of OCS in this population. Principal components analysis suggested two meaningful factors corresponding roughly to obsessions and compulsions. The best-fit model suggested heritabilities of 33 and 26%, respectively. The correlation between additive genetic effects on compulsiveness and obsessiveness was found to be +0.53. Self-report symptoms of obsessions and compulsions in women from the general population are moderately heritable and due, in part, to the same genetic risk factors. An understanding of the etiology of these symptoms is relevant to the study of OCD. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:791-796, 2000.

Influence of ascertainment strategy on finding sex differences in genetic estimates from twin studies of alcoholism

Twin studies have yielded contradictory findings about sex differences in genetic influences on the etiology of alcoholism. Studies based on population registers or epidemiological samples have yielded similar estimates of heritability (50-60% of the total variance) for males and females. In contrast, studies of twins identified through treatment settings have found sizeable genetic contributions to alcoholism in males but usually negligible heritabilities for females. We investigated this discrepancy by applying a "simulated" treatment ascertainment strategy to data on alcohol-related disorders collected by structured interviews with a population-based sample of adult twins aged 18-56 years from the Mid-Atlantic Twin Registry. Structural models were used to estimate heritabilities for two definitions of treatment, and these estimates were compared with those obtained from the population-based sample. In males, heritability estimates were similar across sampling methods, but the treatment ascertainment methods yielded higher estimates of common environmental influences. For females, heritability estimates based on a broad definition of treatment were similar to those obtained by using the random ascertainment design. However, estimates based on sampling women who had been in alcohol-treatment programs were (nonsignificantly) lower than those obtained with the other methods. These results provide partial support for the hypothesis that differences in sampling method may account for differences in heritability estimates for alcoholism among studies of female twins. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:754-761, 2000.

Genetic and environmental influences on juvenile antisocial behaviour assessed on two occasions

BACKGROUND

There is conflicting evidence concerning the magnitude of genetic and shared environmental influences on juvenile antisocial behaviour (AB). The use of more than one assessment of AB may yield more accurate estimates of these influences.

METHODS

Retrospective reports of antisocial behaviour prior to age 18 were obtained on two occasions from a population-based sample of 3522 adult males from male-male twin pairs: phone interviews (wave 1) and self-report questionnaires obtained 19 months later (wave 2). Structural equation modelling estimated the genetic and environmental influences on reliably-measured AB. Factors related to participation of co-twin at wave 1, attrition between waves 1 and 2, and reliability of wave 1 and wave 2 assessments were also investigated.

RESULTS

Twin analyses revealed that genetic, shared environmental, and non-shared environmental influences accounted for approximately 33% (95% CI = 9-57%), 31% (95% CI = 10-51%) and 36% (95% CI = 29-44%) of the variance of reliably measured AB, respectively. We also found significant occasion-specific genetic influences on wave 1 AB. Wave 1 AB did not predict wave 1 participation of co-twin or attrition, but was related to reliability. Co-twins of MZ twins and younger twins were more likely to participate at wave 1; attrition was predicted by being a DZ twin, lack of initial participation of co-twin, fewer years of education, and fewer children. Being older, being unmarried, and having less psychopathology were associated with greater reliability.

CONCLUSIONS

When measurement error is taken into account, both genetic and shared environmental factors are significant influences on juvenile AB, accounting for approximately one-third of variation. The origin of the specific genetic influences on wave 1 AB is unclear, but may be due to factors related to measurement.

Determination of the lowest dilution of aluminium acetate solution able to inhibit in vitro growth of organisms commonly found in chronic suppurative otitis media

Burow's solution has been found to inhibit the in vitro growth of most commonly occurring bacteria found in the discharging ear. These organisms were inoculated onto appropriate agar plates that contained serial dilutions of aluminium acetate. Results show that the lowest dilution able to inhibit the growth of these organisms lies between a 1:80 and a 1:160 dilution of Burow's solution.

Multivariate assessment of factors influencing illicit substance use in twins from female-female pairs

Although familial factors have been shown to influence drug use, abuse, and dependence, little is known about the common and specific factors that influence polysubstance use and misuse. Our objective was to assess whether there are genetic and environmental factors specific to each substance or whether there are factors that predispose an individual to use of illicit substances in general. Twins from female-female pairs from the Virginia Twin Registry were interviewed by phone to assess lifetime nonmedical use of cannabis, sedatives, stimulants, cocaine, opiates, and hallucinogens. Multivariate, biometrical model-fitting was applied to the data using the Mx computer package. In the best-fitting model, use of all classes of drugs was influenced by a single general genetic factor (common to all substances) and a general familial environmental factor. The magnitude of influence of the general genetic factor ranged from 3% of the variance for opiates to 59% of the variance for cannabis. Some differences were seen from the univariate results, indicating some of the parameter estimates were unstable due to small numbers of concordant pairs. However, generalizations could be made. In women, the substances examined share genetic and familial environmental factors which contribute to the vulnerability to use. Degree of influence of the factors differs for the substances examined. However, no specific genetic or familial environmental factors were found to contribute significantly to use of any of the illicit substances.

Childhood sexual abuse and adult psychiatric and substance use disorders in women: an epidemiological and cotwin control analysis

BACKGROUND

Women who report childhood sexual abuse (CSA) are at increased risk for developing psychiatric disorders in adulthood. What is the diagnostic specificity and cause of this association?

METHODS

In a population-based sample of 1411 female adult twins, 3 levels of CSA were assessed by self-report and cotwin report: nongenital, genital, and intercourse. Interviews with twins and parents assessed family background and diagnoses of psychiatric and substance dependence disorders. Odds ratios (ORs) were calculated by logistic regression.

RESULTS

By self-report, 30.4% reported any CSA and 8.4% reported intercourse. Self-reported CSA was positively associated with all disorders, the highest ORs being seen with bulimia and alcohol and other drug dependence. The ORs were modest and often nonsignificant with nongenital CSA and increased with genital CSA and especially intercourse, where most ORs exceeded 3.0. A similar pattern of findings was seen with CSA as reported by the cotwin, although many ORs were smaller. Controlling for family background factors and parental psychopathology produced a small to modest reduction in ORs. In twin pairs discordant for CSA, the exposed twin was at consistently higher risk of illness.

CONCLUSIONS

Women with CSA have a substantially increased risk for developing a wide range of psychopathology. Most of this association is due to more severe forms of CSA and cannot be explained by background familial factors. Although other biases cannot be ruled out, these results are consistent with the hypothesis that CSA is causally related to an increased risk for psychiatric and substance abuse disorders.

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.

Burow's solution in the treatment of active mucosal chronic suppurative otitis media: determining an effective dilution

Burow's solution (13 per cent aluminium acetate) has been found to inhibit in vitro the growth of most commonly occurring bacteria found in the discharging ear. An in vitro study has shown that the minimum inhibitory concentration of Burow's solution for these organisms lies between a 1:80 and a 1:160 dilution. This paper reports on a clinical trial that incorporated 67 discharging ears to establish the most effective strength of aluminium acetate solution. There was no statistical difference in the effectiveness of full strength Burow's solution compared to 3.25 per cent aluminium acetate solution (a quarter strength Burow's solution). Response rates of 80.8 per cent and 75 per cent respectively following a two-week treatment period were achieved using these two solutions. A 1.3 per cent aluminium acetate solution (1/10 strength Burow's solution) was found to be markedly inferior. Bacteriological and audiological profiles were recorded for each patient.

Parenting and adult mood, anxiety and substance use disorders in female twins: an epidemiological, multi-informant, retrospective study

BACKGROUND

Although parenting has long been considered an important risk factor for subsequent psychopathology, most investigations of this question have studied a single informant, clinical populations, one or a few disorders and did not consider relevant covariates.

METHODS

Three dimensions of parenting (coldness, protectiveness and authoritarianism) were measured by combining the retrospective reports from adult female twins, their co-twins, and their mothers and fathers. We assessed by personal interview, lifetime history in the twins of eight common psychiatric and substance abuse disorders and a range of predictors of parenting. Analyses were performed using logistic regression.

RESULTS

Examined individually, high levels of coldness and authoritarianism were modestly but significantly associated with increased risk for nearly all disorders, while the impact of protectiveness was more variable. These associations declined modestly when putative predictors of parenting were added as covariates. Maternal and paternal parenting were equally associated with outcomes in adult daughters. When coldness, protectiveness and authoritarianism were examined together, nearly all significant associations were seen solely with coldness. Few significant interactions were found between maternal and paternal parenting or between coldness, protectiveness and authoritarianism. The shared experience of these three dimensions of parenting predicts a quite small correlation in liability to these disorders in dizygotic twin pairs (e.g. r < 0.04).

CONCLUSION

In women, parenting behaviour, especially levels of coldness, is probably causally related to risk for a broad range of adult psychiatric disorders. The impact of parenting on substance use disorders may be largely mediated through their co-morbidity with major depression, phobias and generalized anxiety disorder. In general population samples, the association of poor parenting with psychiatric illness is modest, largely non-specific and explains little of the observed aggregation of these disorders in families.

Illicit psychoactive substance use, heavy use, abuse, and dependence in a US population-based sample of male twins

BACKGROUND

In order to develop informed approaches to prevention and treatment of illicit psychoactive substance use, abuse, and dependence, we need to understand the sources of individual differences in risk.

METHODS

In personal interviews with 1198 male-male twin pairs (708 monozygotic and 490 dizygotic) ascertained from a population-based registry, we assessed lifetime use, heavy use, and abuse of and dependence on cannabis, sedatives, stimulants, cocaine, opiates, and hallucinogens. Twin resemblance was assessed by probandwise concordance, odds ratio, tetrachoric correlations, and biometrical model fitting.

RESULTS

Twin resemblance for substance use, heavy use, abuse, and dependence was substantial, and consistently greater in monozygotic than in dizygotic twins. For any drug use and for cannabis and hallucinogen use, model fitting suggested that twin resemblance was due to both genetic and familial-environmental factors. Twin resemblance for sedative, stimulant, cocaine, and opiate use, however, was caused solely by genetic factors. With 2 exceptions (cocaine abuse and stimulant dependence), twin resemblance for heavy use, abuse, and dependence resulted from only genetic factors, with heritability of liability usually ranging from 60% to 80%. No consistent evidence was found for violations of the equal environment assumption.

CONCLUSIONS

In accord with prior results in studies of women, the family environment plays a role in twin resemblance for some forms of substance use in men. However, twin resemblance for heavy use, abuse, and dependence in men is largely caused by genetic factors, and heritability estimates are high.

An evaluation of the 'voice test' as a method for assessing hearing in children with particular reference to the situation in developing countries

In developing countries with limited no or access to standard audiometric methods a 'voice test' is a potential non-technological alternative method of assessing hearing. A three level 'voice test' was developed, refined and standardised-accurate response to a whispered voice equating with normal hearing, to a conversational voice with mild hearing loss and to a loud voice to moderate/severe hearing loss. In a hospital based study 177 children were voice tested in sound treated rooms and then tested using standard audiometric procedures to determine precise hearing thresholds. In this situation the voice test had a specificity of 95.9% and a sensitivity of 80%. When the test was evaluated on 201 children aged 3-8 years, first voice tested and then tested with standard audiometry in the classrooms of their pre-primary schools it was found to have a specificity of 97.8% and a sensitivity of 83.3%. With this degree of accuracy in detecting hearing impairment and given the simplicity required to administer the test, it is felt that such a test could be recommended for use by primary health care workers in developing countries where access to standard audiometric methods for assessing hearing are not available.

Chorion type as a possible influence on the results and interpretation of twin study data

The estimation of genetic effects from twin studies usually relies upon the equal environment assumption--that monozygous (MZ) and dizygous (DZ) twin pairs experience equal similarity of their environments from prenatal experiences through adulthood. However, the sharing of a chorion may make a subset of identical twins more similar, or in some cases, more different, than twins that do not share a chorion. Recent studies suggest monochorionic MZ twins resemble one another more than dichorionic MZ twins in cognitive abilities, personality, and risk for psychiatric disorder. To the extent that prenatal environment affects these characteristics, the traditional twin method will yield biased estimates of genetic and environmental influences. We develop models for quantifying this bias and estimating the influence of chorion type on estimates of heritability.

The assessment of dependence in the study of stressful life events: validation using a twin design

BACKGROUND

In the assessment of stressful life events (SLEs), researchers have often tried to evaluate whether individual events are dependent or independent of the respondent's behaviour. We sought to validate this evaluation using a twin methodology. We predicted that dependent SLEs would be more heritable than independent SLEs.

METHODS

We explored, by twin modelling, the resemblance in two pairs of past-year personal and network SLEs rated individually, by trained interviewers, on a four-point dependence-independence scale. We examined results from two waves of interviews with 785 female-female twin pairs ascertained from a population based registry.

RESULTS

Twin model-fitting found no evidence for genetic effects on personal or network independent SLEs. However, familial-environmental factors played an important role in the aetiology of network independent SLEs. For personal and network dependent SLEs, by contrast, three of four analyses suggested a significant aetiological role for genetic factors with estimated heritabilities ranging from 19 to 51%.

CONCLUSIONS

Our results support the validity of interviewer assessments of dependence versus independence of SLEs. As predicted, these assessments were relatively successful at distinguishing SLEs that were influenced by genetic factors from those that were not.

Genetic and environmental risk factors in the aetiology of illicit drug initiation and subsequent misuse in women

BACKGROUND

Subsequent to initial exposure to the use of a psychoactive substance, psychoactive substance use disorder (PSUD) may or may not develop.

AIMS

To investigate the relationship between the risk factors for initiation and the subsequent misuse of psychoactive substances.

METHOD

The lifetime history of illicit substance use and misuse was obtained by telephone interview with 1934 members of female-female twin pairs. We apply a novel model, which estimates the role of genetic and environmental risk factors that influence initiation and those specific to misuse, to three classes of illicit psychoactive substances.

RESULTS

The individual-specific environment and family environment influenced the probability of initiation, but only individual-specific environment had an impact on the probability of subsequent misuse. Genetic factors which influence the risk of initiation and of misuse were identified.

CONCLUSIONS

Aetiological factors that influence drug initiation and subsequent misuse are correlated but not identical. Family environment is an important determinant of risk for drug experimentation. Two classes of genetic risk factors act on the liability to PSUD: those that influence the probability of initiation and those that influence the risk of misuse.

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.

Cholesteatoma in children--the experience at The Red Cross War Memorial Children's Hospital in South Africa 1988-1996

This review of experience with cholesteatoma in children, describes the presentation and features of the disease from a tertiary institution in a 'developing country'. A total of 24 out of 96 cholesteatomas in 81 children (M:F = 44:37) aged 2-12 years initially presented with mastoiditis, with intracranial complications in seven children. Three of the cholesteatomas were congenital, 56 arose from retraction pockets-11 pars flaccida, 45 pars tensa 21 were associated with either a central perforation or total atelectasis and one originated at a ventilation tube site. Open cavity surgery was undertaken in all cases-atticotomy in 14, open mastoid cavity in 82 ears. It was not always possible to preserve reasonably normal pre-operative hearing nor was it possible to improve hearing loss. Twenty-six out of 81 children did not return for follow-up. Even with open cavity surgery, recurrence of cholesteatoma occurred. Late diagnosis, extensive disease, a high rate of complications and poor follow-up are the features of this disease in 'developing' countries.

Causal relationship between stressful life events and the onset of major depression

OBJECTIVE

Stressful life events are associated with the onset of episodes of major depression. However, exposure to stressful life events is influenced by genetic factors, and these factors are correlated with those that predispose to major depression. The aim of this study was to clarify the degree to which stressful life events cause major depression.

METHOD

The authors assessed the occurrence of 15 classes of stressful life events and the onset of DSM-III-R major depression over a 1-year period in female twins ascertained from a population-based registry. The sample contained 24,648 person-months and 316 onsets of major depression. Stressful life events were individually rated on contextual threat and dependence (the degree to which the stressful life event could have resulted from the respondent's behavior). The nature of the relationship between stressful life events and major depression was tested by 1) discrete-time survival analysis examining the relationship between dependence and the depressogenic effect of stressful life events and 2) a co-twin control analysis.

RESULTS

While independent stressful life events were significantly associated with onsets of depression, when level of threat was controlled, the association was significantly stronger for dependent events. The odds ratio for onset of major depression in the month of a stressful life event was 5.64 in all subjects, 4.52 within dizygotic pairs, and 3.58 within monozygotic pairs.

CONCLUSIONS

Stressful life events have a substantial causal relationship with the onset of episodes of major depression. However, about one-third of the association between stressful life events and onsets of depression is noncausal, since individuals predisposed to major depression select themselves into high-risk environments.