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W True

Publications and source records attributed to W True.

12 recordsLinked to original sources
PubMed2001

Genetic and environmental influences on the relationship among combat exposure, posttraumatic stress disorder symptoms, and alcohol use.

The role of genetic and environmental influences on the relationship between combat exposure, posttraumatic stress disorder (PTSD) symptoms, and alcohol use were examined in 4072 male-male twin pairs who served in the United States military during the Vietnam era (1965-1975). Results indicate that the relationship between combat and alcohol use and between PTSD symptom factors and alcohol use were both substantially influenced by genetic factors. Findings are most consistent with a shared vulnerability model for the etiology of the association between PTSD symptoms and alcohol use. Specific unique environmental factors were more important than genetic factors for PTSD symptoms, and both factors were equally important for alcohol use. Further support is also found for the role of the unique environment in PTSD symptoms.

Alcoholism↗
PubMed2000

Lifetime prevalence of mood and anxiety disorders in twin pairs discordant for schizophrenia.

There have been long questions about the relationship of schizophrenia to other mental disorders. Lifetime DSM-III-R diagnoses of mood and anxiety disorders in twins with clinically diagnosed schizophrenia (n = 24) and their non-affected co-twins (n = 24) were compared with twins from pairs without schizophrenia (n = 3327) using a sample from the Vietnam Era Twin Registry. Schizophrenic probands had significantly elevated rates of all included disorders (bipolar disorder, major depression, dysthymia, generalized anxiety disorder, panic disorder, and PTSD) compared with controls (P<0.01). The odd ratios comparing co-twins of schizophrenic probands with controls was greater than three for every disorder, but did not attain statistical significance. A similar pattern was observed when analyses were restricted to only monozygotic twins (n = 12). Consistent with other studies, schizophrenics appeared to have higher rates of a range of mental disorders. Our results suggest that schizophrenia per se represents a risk factor for other psychiatric disorders, but the absence of significantly elevated risk among non-schizophrenic co-twins suggested that family environmental and/or genetic factors that contribute to risk of schizophrenia do not increase the risk of mood and anxiety disorders to the same extent that the risk of these other disorders is increased by the presence of schizophrenia.

Adult↗
PubMed1998

Co-occurrence of abuse of different drugs in men: the role of drug-specific and shared vulnerabilities.

BACKGROUND: Previous research has demonstrated genetic and environmental influences on abuse of individual substances, but there is less known about how these factors may influence the co-occurrence of abuse of different illicit drugs. METHODS: We studied 3372 male twin pairs from the Vietnam Era Twin Registry. They were interviewed using the Diagnostic Interview Schedule, Version III, Revised to investigate the extent to which the abuse of different categories of drugs occurs together within an individual, as well as the possibility that genetic and environmental factors are responsible for observed co-occurrence. Co-occurrence was quantified using odds ratios and conditional probabilities. Multivariate biometrical modeling analyses were used to assess genetic and environmental influences on co-occurrence. RESULTS: Abusing any category of drug was associated with a marked increase in the probability of abusing every other category of drugs. We found evidence for a shared or common vulnerability factor that underlies the abuse of marijuana, sedatives, stimulants, heroin or opiates, and psychedelics. This shared vulnerability is influenced by genetic, family environmental, and nonfamily environmental factors, but not every drug is influenced to the same extent by the shared vulnerability factor. Marijuana, more than other drugs, was influenced by family environmental factors. Each category of drug, except psychedelics, had genetic influences unique to itself (ie, not shared with other drug categories). Heroin had larger genetic influences unique to itself than did any other drug. CONCLUSION: There are genetically and environmentally determined characteristics that comprise a shared or common vulnerability to abuse a range of illicit drugs.

Adult↗
PubMed1998

A registry-based twin study of depression in men.

BACKGROUND: The only large, registry-based twin study of depression using diagnostic criteria assessed by structured interview included only women. We present results from a comparable study of men. METHODS: Data were collected using a standardized telephone interview of men from the Vietnam Era Twin Registry. Both twins from 3372 pairs participated. Proband-wise concordance rates and biometric modeling were used to analyze the data. RESULTS: The diagnosis of major depression (MD), as defined by DSM-III-R, and the subtype of severe/psychotic MD were significantly affected by genetic (h2=0.36 and 0.39, respectively) and nonshared environmental (e2=0.64 and 0.61, respectively) factors but not by family environmental factors. Dysthymia and mild and moderate MD were affected by family environmental (c2=0.27, 0.08, and 0.14, respectively) and nonshared environmental (e2=0.73, 0.92, and 0.86, respectively) factors but not by genetic factors. Early-onset (before age 30 years) and late-onset (after age 30 years) MD were significantly affected by genetic (h2=0.47 and 0.10, respectively) and nonshared environmental (e2=0.53 and 0.90, respectively) factors. Early-onset MD was significantly more heritable than late-onset MD. CONCLUSIONS: The magnitude of genetic and environmental effects on depression in men is similar to that previously reported in women. Also similar to previous findings, more severe and earlier-onset depression may be more strongly affected by genetic factors, but differences in the reliability of reports of depression associated with severity may inflate estimates of the effect of the unique environment and deflate heritability estimates for less severe depression.

Adult↗
PubMed1996

Genetic influences on DSM-III-R drug abuse and dependence: a study of 3,372 twin pairs.

Research and clinical experience indicate that drug use disorders tend to run in families. The objective of this study was to distinguish between the family environment and genetic factors as the source of this observed family resemblance. Data were collected by telephone interview from members of the Vietnam Era Twin Registry, comprising male twin pairs who served in the U.S. military between 1965 and 1975. There were 3,372 pairs in which both twins participated. Drug use disorder was defined as receiving a diagnosis of drug abuse or dependence according to DSM-III-R; 10.1% of the sample had abused or been dependent on at least one illicit drug. A significant difference between concordance rates for monozygotic (26.2%) vs. dizygotic (16.5%) twins indicated a genetic influence on drug use disorder. Biometrical modeling indicated that genetic factors (34% of the variance), the environment shared by twins (28% of the variance), and the nonshared environment (38% of the variance) had significant influences of similar magnitudes on the individual's risk of developing a drug use disorder. These results support the application of molecular genetic approaches to elucidate the genetic influence on drug use disorder, as well as the potential efficacy of environmental intervention to reduce risk.

Adult↗
PubMed1993

A strategy for assembling samples of adult twin pairs in the United States.

In this paper we develop a methodology for the identification of large numbers of U.S. adult twin pairs. Data for this study derive from the U.S. Department of Defense and the Vietnam Era Twin (VET) Registry. The Department of Defense identified potential male twins (n = 10,002) using a computerized record linkage algorithm based on the same last name, same date of birth, and the same first five digits of the Social Security number. Twinship was confirmed by comparison with the Vietnam Era Twin Registry. We developed a logistic regression model that predicts the probability that a paired record identifies twins based on the absolute difference in the last four digits in the Social Security number, the age of issuance of the Social Security number, and the frequency of occurrence of the last name. We used the estimated coefficients derived from this regression model to assign predicted probabilities of being a twin to each matched record. There is a close correspondence between the observed and expected number of twins when evaluated across deciles of predicted probabilities of being a twin; the value of the Harrell's c index (c = 0.68 +/- 0.0004) indicates the overall predictive accuracy of the regression equation. The results from this study demonstrate the feasibility of identifying adult male-male twin pairs from any large computerized database that contains name, date of birth and Social Security number. However, the selection criteria used in the creation of the computer database must be clearly specified to avoid constructing a biased sample of twins.

Adult↗
PubMed1993

Do genes influence exposure to trauma? A twin study of combat.

Data from 4,029 male-male twin pairs who served in the United States military during the Vietnam era (1965-1975) were used to examine genetic and non-genetic factors that influence wartime exposure to traumatic events. Specific events examined were volunteering for service in Vietnam, actual service in Southeast Asia, a composite index of 18 combat experiences, and information from military records about being awarded combat decorations. Correlations within monozygotic (MZ) and dizygotic (DZ) twin pairs for volunteering for service in Vietnam were 0.40 and 0.22, respectively. For actually serving in Southeast Asia, the MZ correlation was 0.41 and the DZ correlation was 0.24. Analysis of twin pairs in which both siblings served in Southeast Asia (n = 820) demonstrated a correlation for self-reported combat experiences within MZ and DZ pairs of 0.53 and 0.30, respectively. Heritability estimates ranged from 35 to 47%. The family environment did not have a significant effect on any of the variables. Analyses of data from military records regarding being awarded a combat decoration provided very similar results to those found for self-reported combat experiences.

Adult↗
PubMed1992

Elementary methods for the analysis of dichotomous outcomes in unselected samples of twins.

This paper presents an elementary statistical method for analyzing dichotomous outcomes in unselected samples of twin pairs using stratified estimators of the odds ratio. The methodology begins by first randomly designating one member of each twin pair as an "index" twin and the other member as the "co-twin." Stratifying on zygosity, odds ratios are used to measure the association between disease in the index twin and disease in the co-twin. From these zygosity-specific tables we calculate the Woolf-Haldane estimator of the common odds ratio (psi F, the weighted average of the zygosity-specific odds ratios), the Mantel-Haenszel test statistic (chi 2M-H) for the common odds ratio, and a test (chi 2G) for the difference in the zygosity-specific odds ratios. In this application, psi F provides an estimate of the familial association for disease and the accompanying chi 2M-H provides a test of the null hypothesis, psi F = 1 (i.e., there is no evidence for a familial influence on disease). The chi 2G is a test of the null hypothesis that psi MZ = psi DZ; a significant value for chi 2G suggests a genetic influence on disease (assuming that the observed odds ratios follow a pattern where psi MZ greater than psi DZ). A new test statistic (chi 2c) is proposed that incorporates the expectation that psi MZ = psi 2DZ under a purely additive genetic model with no common environmental effects. A significant value of chi c2 indicates that the different odds ratios across zygosity are partly due to common environmental influences. Conversely, a nonsignificant value of chi 2c is an indication that the zygosity-specific odds ratios are due solely to additive genetic effects and not to common environment. This basic approach is extended to examine the effects of measured indicators of the specific environment and the assessment of certain forms of gene by environment interaction. All of the methods are easily understood, highly flexible, readily computed using a hand calculator, and incorporate the inherent genetic information contained within twin samples.

Data Interpretation, Statistical↗
PubMed1989

Determining zygosity in the Vietnam Era Twin Registry: an approach using questionnaires.

The Vietnam Era Twin Registry (VETR) is a registry of 7375 American male veteran twin pairs born between 1939 and 1955 who served in the armed forces of the United States between 1964 and 1975. Optimal use of registry data requires the determination of zygosity. Two approaches are available: analysis of blood genetic marker systems and responses of twins to questions about sibling similarity. Zygosity for the VETR was determined using the questionnaire technique supplemented with blood group typing data abstracted from military records. After comparing four alternative zygosity assignment methods, a logistic regression technique which uses discriminating variables based on race was selected. The approach is similar to that described by Magnus et al. (1983) in their study of Norwegian twins, suggesting that questionnaire responses are independent of nationality and reinforcing the reliability of the questionnaire method for zygosity ascertainment.

Adult↗
PubMed1987

The Vietnam Era Twin (VET) Registry: method of construction.

A Vietnam Era (1964-1975) Twin Registry of American male-male veterans born between 1939 and 1955 has been developed to provide a study sample for research evaluating the impact of Vietnam service on the medical and psychosocial aspects of health. In preparation for developing the Registry, several alternative sources of twins and methods for identifying twins were investigated. A computerized database of veterans discharged from the military after 1967 was selected as the source because it contains about 50% of the total Vietnam era veteran population, is reasonably unbiased, and provides a feasible method for identifying twins. Twins were identified using an algorithm which involved matching entries on the database for same last name, different first name, same date of birth, and similar social security number. Twin status was confirmed by review of military records. The registry, now complete, is composed of 7,400 twin pairs. It will be an important resource for future research projects.

Adult↗
PubMed1987

The Vietnam Era Twin (VET) Registry: ascertainment bias.

An examination of ascertainment bias in identification of twin pairs in the Vietnam Era Twin Registry has been conducted. A complete listing of all male-male Vietnam era veteran twin pairs born in Connecticut between 1939 and 1955 was obtained (N = 150). An attempt was made to match these pairs with a listing of Vietnam era veteran twin pairs derived from the United States Department of Defense's Defense Manpower Data Center (DMDC) computer files. The results indicate that the DMDC files identified only 46.7% of the 150 Connecticut born Vietnam era veteran pairs. Statistically significant differences (P less than 0.05) between pairs found on the DMDC files and Connecticut veteran pairs missing from the DMDC files are observed for the following variables: a) year of discharge from military service, b) total length of active military service, c) branch of service, and d) foreign service. No consistent pattern of bias is observed for factors related to the physical and psychosocial health of veteran pairs. The implications of the ascertainment biases in the Vietnam Era Twin Registry are discussed.

Adult↗