Specificity of familial vulnerability for alcoholism versus major depression in men

There are various hypotheses regarding comorbidity between alcohol dependence (AD) and major depression (MD). We interviewed 3372 pairs of male twins assessing DSM-III-R MD and AD. Individuals with comorbid MD and AD exhibited greater severity of each disorder than individuals with only one. MD in one twin was associated with risk of MD alone and MD plus AD, but not AD alone in the cotwin. AD in one twin was associated with risk of AD alone and AD plus MD, but not MD alone in the cotwin. The best fitting biometrical comorbidity model was the reciprocal causation model in which AD can cause MD and vice versa. However, a model in which genetic and environmental influences on each disorder were correlated could not be definitively rejected. Our data are most consistent with a mechanism of reciprocal causation, whereby MD increases risk for AD and AD increases risk of MD.

Posttraumatic stress disorder and late-onset smoking in the Vietnam era twin registry

Epidemiological and clinical studies have consistently reported associations between smoking and posttraumatic stress disorder (PTSD). This study analyzed diagnostic interview data on 6,744 members of the Vietnam Era Twin Registry to clarify the PTSD-smoking relation and to examine whether genetic liability for smoking moderated this relation. Preexisting active (unremitted) PTSD increased risk of late-onset daily smoking. Remitted PTSD decreased risk. Active PTSD increased risk of smoking at all levels of genetic liability; the effect was strongest for those with least genetic liability. This suggests PTSD represents a nongenetic pathway to late-onset smoking among individuals who were nonsmokers prior to developing PTSD. If replicated, these results identify PTSD as a risk factor for smoking that should lead to early tobacco control treatment in this population.

A twin registry study of the relationship between posttraumatic stress disorder and nicotine dependence in men

CONTEXT

Recent studies indicate a strong association between posttraumatic stress disorder (PTSD) and nicotine dependence (ND). However, the explanation for the association remains unclear.

OBJECTIVE

To test competing explanations for the association between PTSD and ND.

DESIGN, SETTING, AND PARTICIPANTS

Analysis of data on 6744 members of the Vietnam Era Twin Registry, a national registry of all male-male twin pairs who served in the military during the Vietnam era interviewed in 1991-1992.

MAIN OUTCOME MEASURES

Risk of PTSD and ND using the Diagnostic Interview Schedule for the DSM-III-R.

RESULTS

The prevalence of ND was elevated among trauma-exposed individuals (52.0%) and those with PTSD (71.7%) compared with unexposed individuals (40.5%). This association was significant for ND and for trauma without PTSD (odds ratio, 1.31; 95% confidence interval [CI], 1.18-1.45) and for PTSD (odds ratio, 2.34; 95% CI, 1.92-2.84) and was not entirely explained by shared risk factors. Shared genetic effects explained 63% of the PTSD-ND association; the remaining covariance was explained by individual-specific environmental effects. Using survival analysis with time-dependent covariates, ND was associated with a substantially increased risk of PTSD among trauma-exposed men (hazard ratio, 1.98; 95% CI, 1.61-2.42). Trauma (hazard ratio, 1.49; 95% CI, 1.35-1.64) and PTSD (hazard ratio, 1.36; 95% CI, 1.14-1.61) were less strongly but significantly associated with increased risk of ND onset after controlling for shared risk factors.

CONCLUSIONS

Most of the PTSD-ND association is explained by shared genetic effects. However, there is a substantial, robust PTSD-ND association not explained by shared risk factors. Multiple explanations for the association were supported; however, the strongest association was consistent with preexisting ND increasing the risk of PTSD onset. These data suggest that male veterans with a history of ND may be at increased risk for PTSD. Further research on the biological mechanisms underlying PTSD-ND comorbidity is needed.

Subjective reactions to cocaine and marijuana are associated with abuse and dependence

Subjective effects of marijuana and cocaine use are associated with amount of drug use and potentially with risk of abuse and dependence. We used Latent Class Analyses (LCA) to examine subjective responses to two categories of drugs and link these to abuse and dependence. In 1992, subjective responses were queried of 2506 marijuana and 661 cocaine lifetime users who were members of the Vietnam Era Twin Registry. LCA was used to identify classes of subjective effects. Multinomial logistic regression models were computed to test for an association between classes and marijuana and cocaine abuse or dependence. The best LCA solution for marijuana identified 6 distinct classes characterized as positive, relaxed, reactive, adverse, low and very reactive. The best LCA solution for cocaine identified 5 distinct classes characterized as positive, alert, adverse, low and very reactive. Marijuana abuse and dependence were significantly associated with each latent class. Cocaine abuse was associated with the reactive class (OR=3.9; 95% CI: 1.6-9.5). Cocaine dependence was associated with reactive (OR=15.3; 95% CI: 7.1-32.6), adverse (OR=9.7; 95% CI: 4.5-21.0) and very reactive (OR=18.7; 95% CI: 5.6-62.6) classes. We found evidence for both qualitative and quantitative subjective effect profiles. Subjective effects, both positive and adverse are associated with lifetime risk for marijuana and cocaine dependence.

Latent class typology of nicotine withdrawal: genetic contributions and association with failed smoking cessation and psychiatric disorders

BACKGROUND

Nicotine withdrawal is associated with failed smoking cessation and thus contributes to continuance of the habit and increases risk of smoking-related illnesses. Withdrawal is also associated with psychiatric disorders such as depression and alcoholism. However, relatively little is known about how to characterize the severity of withdrawal, including whether withdrawal subtypes exist in male smokers. If so, do these subtypes represent quantitative or qualitative differences?

METHOD

Smoking and withdrawal data were obtained from 4112 male-male twin pairs of the Vietnam Era Twin Registry during a 1992 administration of the Diagnostic Interview Schedule. Latent Class Analysis (LCA) was used to derive significantly different nicotine withdrawal profiles, and their association with psychiatric disorders was assessed. Genetic and environmental contributions and the correlation between these contributions were evaluated using bivariate biometrical modeling of the withdrawal phenotype and failed smoking cessation.

RESULTS

The LCA model which best fit the data was a four-class severity continuum. Psychiatric disorders were significantly associated with more severe classes and the magnitude of the association increased as withdrawal severity increased. Genetics accounted for 31% and 51% of the variance in risk for withdrawal and failed cessation, respectively. The genetic contributions were significantly correlated (r = 0.37).

CONCLUSIONS

Nicotine withdrawal classes are characterized by quantitative differences. The strong association between psychiatric disorders and withdrawal severity and the significant genetic correlation between withdrawal and cessation highlight the importance of withdrawal severity. Further refinement of the DSM definition of withdrawal to incorporate severity ratings may be warranted.

Agoraphobic behavior and panic attack: a study of male twins

We used data from 3372 pairs of male twins from the Vietnam Era Twin Registry to examine comorbidity and familial influences on the frequently observed association between agoraphobic behavior and panic. Due to low prevalence of DSM-III-R-defined panic disorder, we also examined subjects who had experienced at least one panic attack during their lives. Agoraphobic behavior among individuals with a history of panic attacks showed familial aggregation (odds ratio = 5.7; P = .018 ). Probands with panic attacks and agoraphobic behavior and their co-twins had higher risk of major depression than probands without agoraphobic avoidance and their co-twins (P = .01). Groups did not differ for alcohol dependence or antisocial personality. Agoraphobic behavior associated with panic attack is familial and associated with comorbid major depression. Agoraphobia following panic attack does not seem to reflect severity as agoraphobic behavior in the proband was unrelated to risk of panic attacks in the co-twin.

Juvenile conduct disorder as a risk factor for trauma exposure and posttraumatic stress disorder

Juvenile conduct disorder (CD) is a well-documented risk factor for posttraumatic stress disorder (PTSD). This study examines the mechanisms underlying this relationship by using data from 3,315 twin pairs in the Vietnam Era Twin Registry. Results indicate the number of conduct disorder symptoms increased risk of trauma exposure and PTSD in a dose-response fashion. This increased risk was mediated in part by the positive association between CD and lifestyle factors and was not due to confounding by shared genetic or familial vulnerability. The findings suggest CD increases risk for trauma exposure and PTSD among male veterans through direct and indirect mechanisms. Veterans who have a history of CD are at high risk for trauma exposure and development of PTSD.

A twin study of depression symptoms, hypertension, and heart disease in middle-aged men

OBJECTIVE

Epidemiological and clinical studies have established an association between major depression and cardiovascular disease. We utilized a twin design to test whether there are common genetic and environmental risk factors underlying depression symptoms, hypertension and heart disease.

METHODS

Association studies were conducted with 6,903 male-male twins from the Vietnam Era Twin Registry who responded to both a 1990 health questionnaire and a 1992 telephone administration of a structured psychiatric interview. Data from 2,731 complete twin pairs were used to fit genetic models which determined the extent to which lifetime depression symptoms, heart disease and hypertension shared genetic and/or environmental factors.

RESULTS

Heart disease was significantly associated with 1-4 symptoms and 5 or more symptoms of depression (odds ratio [OR] = 2.62; 95% confidence interval [CI]: 1.54-4.46 and OR = 4.02; 95% CI: 2.16-7.46). Hypertension was significantly associated with 1 to 4 symptoms and 5 or more symptoms of depression (OR = 1.29; 95% CI: 1.11-1.50 and OR = 1.49; 95% CI: 1.21-1.83). The genetic correlations were significant between depression symptoms and hypertension (r =.19), and between depression symptoms and heart disease (r =.42). Of the total variance in depression, 8% was common to hypertension and heart disease, 7% of the variance in hypertension was common with depression symptoms and heart disease, and 64% of the variance in heart disease was common with depression symptoms and hypertension.

CONCLUSIONS

Men who reported cardiovascular disease were significantly more likely to have depression symptoms. The lifetime co-occurrence of these phenotypes is partly explained by common genetic risk factors.

The heritability of failed smoking cessation and nicotine withdrawal in twins who smoked and attempted to quit

The magnitude of the association between nicotine withdrawal and failed smoking cessation remains uncertain, and the potential genetic contribution to that relationship is unknown. We used a twin design study to test if genetic and environmental risk factors contribute to nicotine withdrawal and failed cessation. We then estimated the magnitude of genetic and environmental risk factors and the associated correlations. Cigarette consumption data were obtained in 1992 from 4,112 (1,806 pairs, 496 singletons) male twin pairs from the Vietnam Era Twin Registry. Participants responded to a telephone administration of the Diagnostic Interview Schedule. Odds ratios were computed for failed smoking cessation as a function of 12 individual nicotine withdrawal symptoms. Genetic model fitting was performed on a sample of 1818 twin pairs, all of whom were lifetime smokers; both twins of the pairs had made at least one quit attempt. After adjustment for cigarette consumption, odds of failed smoking cessation ranged from.87 (95% CI.76-.99) for "increased appetite/weight gain" to 1.85 (95% CI 1.55-2.22) for "depressed." Genetic influences accounted for 54% and 29.7% of the variance in risk for failed smoking cessation and nicotine withdrawal, respectively. The correlation between genetic influences was significant (r=.31, 95% CI.17-.45). The magnitude of the association between failed cessation and nicotine withdrawal varied by symptom. The risk of experiencing nicotine withdrawal after a quit attempt was related partly to genetic vulnerability; lifetime risk for both failed cessation and nicotine withdrawal was related partly to genetic factors that were correlated.

Nicotine and familial vulnerability to schizophrenia: a discordant twin study

Tobacco use is significantly associated with schizophrenia. However, it is not clear if smoking is associated with the illness itself, treatment, or underlying vulnerability to the disease. Smoking was studied in a sample of schizophrenic probands (n = 24), their unaffected co-twins (n = 24), and controls (n = 3,347). Unaffected co-twins had higher rates of daily smoking than controls. Probands and co-twins were more frequently unsuccessful in attempts to quit than controls. Probands reported shaky hands and depression following smoking cessation more often than controls, whereas unaffected co-twins reported difficulty concentrating, drowsiness, nervousness, and headache following smoking cessation more often than controls. Results are consistent with the hypothesis that nicotine use is influenced by familial vulnerability to schizophrenia, not just clinical schizophrenia per se.

Nicotine and familial vulnerability to schizophrenia: a discordant twin study

Tobacco use is significantly associated with schizophrenia. However, it is not clear if smoking is associated with the illness itself, treatment, or underlying vulnerability to the disease. Smoking was studied in a sample of schizophrenic probands (n = 24), their unaffected co-twins (n = 24), and controls (n = 3,347). Unaffected co-twins had higher rates of daily smoking than controls. Probands and co-twins were more frequently unsuccessful in attempts to quit than controls. Probands reported shaky hands and depression following smoking cessation more often than controls, whereas unaffected co-twins reported difficulty concentrating, drowsiness, nervousness, and headache following smoking cessation more often than controls. Results are consistent with the hypothesis that nicotine use is influenced by familial vulnerability to schizophrenia, not just clinical schizophrenia per se.

A twin registry study of familial and individual risk factors for trauma exposure and posttraumatic stress disorder

This study examines the association of individual and familial risk factors with exposure to trauma and posttraumatic stress disorder (PTSD) in male twins (N = 6744) from the Vietnam Era Twin Registry. Independent reports of familial psychopathology from co-twins were used to avoid the potential biases of the family history method. Risk for exposure to traumatic events was increased by service in Southeast Asia, preexisting conduct disorder, preexisting substance dependence, and a family history of mood disorders whose effects appear to be partly genetic. Preexisting mood disorders in the individual were associated with decreased odds of traumatic exposure. Risk of developing PTSD following exposure was increased by an earlier age at first trauma, exposure to multiple traumas, paternal depression, less than high school education at entry into the military, service in Southeast Asia, and preexisting conduct disorder, panic disorder or generalized anxiety disorder, and major depression. Results suggest the association of familial psychopathology and PTSD may be mediated by increased risk of traumatic exposure and by preexisting psychopathology.

A twin study of generalized anxiety disorder symptoms, panic disorder symptoms and post-traumatic stress disorder in men

Generalized anxiety disorder (GAD), panic disorder (PD) and post-traumatic stress disorder (PTSD) often co-occur. We investigated whether and to what degree genetic and environmental contributions overlap among symptoms of GAD, symptoms of PD and PTSD. Subjects were 3327 monozygotic and dizygotic male-male twin pair members of the Vietnam Era Twin Registry who participated in a 1992 telephone administration of the Diagnostic Interview Schedule Version 3 Revised (DIS3R). Genetic model fitting was performed to estimate the magnitude of genetic and environmental contributions to the lifetime co-occurrence of GAD symptoms, PD symptoms and PTSD. The liability for GAD symptoms was due to a 37.9% additive genetic contribution common to PD symptoms and PTSD. Liability for PD symptoms was due to a 20.7% additive genetic contribution common to GAD symptoms and PTSD, and a 20.1% additive genetic influence specific to PD symptoms. Additive genetic influences common to symptoms of GAD and PD accounted for 21.3% of the genetic variance in PTSD. Additive genetic influences specific to PTSD accounted for 13.6% of the genetic variance in PTSD. Remaining variance for all three disorders was due to unique environmental factors both common and specific to each phenotype. These results suggest that these disorders each have etiologically distinct components and also have significant genetic and unique environmental contributions in common.

A twin study of the association between pathological gambling and antisocial personality disorder

Many individuals with a history of pathological gambling (PG) also have a history of engaging in antisocial behaviors, and this has often been interpreted as a result of the former causing the latter. In a sample of 7,869 men in 4,497 twin pairs from the Vietnam Era Twin Registry, the authors examined (a) the association between PG and antisocial personality disorder (ASPD), (b) the extent to which PG might be differentially associated with childhood conduct disorder (CD) and adult antisocial behavior (AAB), and (c) the contribution of genetic and environmental factors to the association of PG with ASPD, CD, and AAB. PG was significantly associated with all 3 antisocial behavior disorders, and the association of PG with ASPD, CD, and AAB was predominantly explained by genetic factors. The results of this study suggest that the greater-than-chance co-occurrence of PG and antisocial behavior disorders is partially due to their sharing a common genetic vulnerability. The antisocial behavior observed among many individuals with PG probably cannot be interpreted as being simply a consequence of the PG.

A twin study of the association between pathological gambling and antisocial personality disorder

Many individuals with a history of pathological gambling (PG) also have a history of engaging in antisocial behaviors, and this has often been interpreted as a result of the former causing the latter. In a sample of 7,869 men in 4,497 twin pairs from the Vietnam Era Twin Registry, the authors examined (a) the association between PG and antisocial personality disorder (ASPD), (b) the extent to which PG might be differentially associated with childhood conduct disorder (CD) and adult antisocial behavior (AAB), and (c) the contribution of genetic and environmental factors to the association of PG with ASPD, CD, and AAB. PG was significantly associated with all 3 antisocial behavior disorders, and the association of PG with ASPD, CD, and AAB was predominantly explained by genetic factors. The results of this study suggest that the greater-than-chance co-occurrence of PG and antisocial behavior disorders is partially due to their sharing a common genetic vulnerability. The antisocial behavior observed among many individuals with PG probably cannot be interpreted as being simply a consequence of the PG.

Traumatic brain injury and schizophrenia in members of schizophrenia and bipolar disorder pedigrees

OBJECTIVE

Schizophrenia following a traumatic brain injury could be a phenocopy of genetic schizophrenia or the consequence of a gene-environment interaction. Alternatively, traumatic brain injury and schizophrenia could be spuriously associated if those who are predisposed to develop schizophrenia have greater amounts of trauma for other reasons. The authors investigated the relationship between traumatic brain injury and psychiatric diagnoses in a large group of subjects from families with at least two biologically related first-degree relatives with schizophrenia, schizoaffective disorder, or bipolar disorder.

METHOD

The Diagnostic Interview for Genetic Studies was used to determine history of traumatic brain injury and diagnosis for 1,275 members of multiplex bipolar disorder pedigrees and 565 members of multiplex schizophrenia pedigrees.

RESULTS

Rates of traumatic brain injury were significantly higher for those with a diagnosis of schizophrenia, bipolar disorder, and depression than for those with no mental illness. However, multivariate analysis of within-pedigree data showed that mental illness was related to traumatic brain injury only in the schizophrenia pedigrees. Independent of diagnoses, family members of those with schizophrenia were more likely to have had traumatic brain injury than were members of the bipolar disorder pedigrees. The members of the schizophrenia pedigrees also failed to show the gender difference for traumatic brain injury (more common in men than in women) that was expected and was present in the bipolar disorder pedigrees. Subjects with a schizophrenia diagnosis who were members of the bipolar disorder pedigrees (and thus had less genetic vulnerability to schizophrenia) were less likely to have had traumatic brain injury (4.5%) than were subjects with schizophrenia who were members of the schizophrenia pedigrees (and who had greater genetic vulnerability to schizophrenia) (19.6%).

CONCLUSIONS

Members of the schizophrenia pedigrees, even those without a schizophrenia diagnosis, had greater exposure to traumatic brain injury compared to members of the bipolar disorder pedigrees. Within the schizophrenia pedigrees, traumatic brain injury was associated with a greater risk of schizophrenia, consistent with synergistic effects between genetic vulnerability for schizophrenia and traumatic brain injury. Posttraumatic-brain-injury schizophrenia in multiplex schizophrenia pedigrees does not appear to be a phenocopy of the genetic disorder.

Genetic and environmental influences on posttraumatic stress disorder, alcohol and drug dependence in twin pairs

We investigated whether and to what degree genetic and environmental contributions overlap among posttraumatic stress disorder (PTSD), alcohol dependence (AD) and drug dependence (DD). Subjects were 3304 monozygotic and dizygotic male-male twin pair members of the Vietnam Era Twin Registry who participated in 1992 telephone administration of the Diagnostic Interview Schedule Version 3 Revised (DIS-3R). Genetic model fitting was performed to estimate the magnitude of genetic and environmental contributions to the lifetime co-occurrence of DSM-III-R PTSD, AD and DD. The liability for PTSD was partially due to a 15.3% genetic contribution common to AD and DD and 20.0% genetic contribution specific to PTSD. Risk for AD was partially due to a 55.7% genetic contribution common to PTSD and DD. Genetic influences common to PTSD and AD accounted for 25.2% of the total risk for DD. Specific family environmental influence accounted for 33.9% of the total variance in risk for DD. Remaining variance for all three disorders was due to unique environmental factors both common and specific to each phenotype. These results suggest that PTSD, AD and DD each have etiologically distinct components and also have significant genetic and unique environmental contributions in common.

Common genetic vulnerability for pathological gambling and alcohol dependence in men

BACKGROUND

In comparison with alcohol dependence (AD), relatively little is known about the causes of pathological gambling (PG). Given the high rate of comorbidity between PG and AD, knowledge about the causes of AD may be applied to understanding those of PG.

METHODS

Subjects were adult male twin pairs from the Vietnam Era Twin Registry. Lifetime histories of PG and AD were assessed by structured psychiatric telephone interview. The validity of a continuum of PG liability was tested to determine whether the causes of subclinical PG, or problem gambling, are quantitatively or qualitatively distinct from those of DSM-III-R PG disorder. Genetic model-fitting methods were used to quantify the extent to which the genetic and environmental risk for PG could be explained by the risk for AD.

RESULTS

Tests of the continuity model of PG were all consistent with the hypothesis that subclinical PG and DSM-III-R PG disorder have many, perhaps all, of the same risk factors and thus differ quantitatively rather than qualitatively. Depending on the PG definition, between 12% and 20% of the genetic variation and between 3% and 8% of the nonshared environmental variation in the risk for PG were accounted for by the risk for AD.

CONCLUSIONS

Subclinical PG, or problem gambling, may be a milder form of PG, rather than an etiologically distinct syndrome. Risk for AD accounts for a significant but modest proportion of the genetic and environmental risk for subclinical PG and DSM-III-R PG disorder.

Strategies for improving comorbidity measures based on Medicare and Medicaid claims data

Claims-based measures of comorbid illness severity have generally relied on the diagnoses listed for a single hospitalization. Unfortunately, such diagnostic information is often limited because patients have not been hospitalized during periods of interest, because of incomplete coding of diagnoses on claims forms, or because listed diagnoses represent complications of the hospitalization rather than pre-existing comorbid conditions. To address these limitations, we developed and tested four comorbidity index scores for patients with breast cancer, each based on different sources of health services claims from Medicare and Medicaid: hospitalization for breast cancer surgery; outpatient care prior to the hospitalization; other inpatient care prior to the hospitalization; and all sources combined. Varying the number and type of sources of diagnostic information yielded only very small improvements in the prediction of mortality at 1 and 3 years. Surprisingly, even simpler measures of comorbidity (crude number of diagnoses) and of prior health care utilization (total days spent in the hospital) performed at least as well in predicting mortality as did the more complex index scores which assigned points and weights for specific conditions. The greatest improvement in explanatory power was observed when another source of clinical information (cancer stage derived from a population-based cancer registry) was used to supplement claims information. Expanding the source of claims diagnoses and focusing on time periods prior to an index hospitalization are insufficient for substantially improving the explanatory power of claims-based comorbidity indices. Other improvements suggested by our results should include: increasing the completeness and accuracy of claims diagnoses; supplementing diagnoses with health care utilization information in claims data; and supplementing claims data with other sources of clinical information.

Impaired verbal memory is associated with impaired motor performance in schizophrenia: relationship to brain structure

Deficient ability to take advantage of predictable elements in the performance of cognitive tasks has been proposed as an underlying factor for a number of deviances in schizophrenia. In a schizophrenic sample (n=39), we propose and test the view that certain memory and motor anomalies arise because of a compromise in the capacity to take advantage of the redundant (predictable) features of cognitive tasks. Results demonstrate a relationship between reduced capacity to take advantage of predictable features of two different cognitive processing tasks, one verbal memory, and the other motor. Poorer verbal recall on high-redundancy word lists was associated with a reduced ability to produce synchronous finger tapping in response to a high redundancy auditory stimulus, and inversely correlated with formal thought disorder ratings. These relationships, we suggest, reflect a specific and common schizophrenic deficit in the use of redundancies, not attributable to a generalized deficiency in performance. Structural imaging evidence from a subsample of these subjects (n=16) implicates frontal areas as the locus of this cognitive impairment.

Schizophrenia: genes and environment

The historical and genetic foundations of our current understanding of schizophrenia are reviewed, as are the present and future directions for research. Genetic epidemiological investigations, including family, twin, and adoption studies have confirmed the contributions of genetic and environmental determinants of schizophrenia. For example, identical twins show average concordance rates of only 50%; rates of 100% would be expected on the basis of genetic equivalence alone. Genetic factors may cause errors in brain development and synaptic connections. A broad range of environmental components may further damage the brain. Biological components may include pregnancy and delivery complications, such as intrauterine fetal hypoxia, infections, and malnutrition. Primarily nonbiological components may include psychosocial stressors, such as residence in an urban area and dysfunctional family communication. It is likely that the environmental factors interact with the genetic liability in a negative manner to produce disorders in the schizophrenic spectrum. Genetic and environmental components of the disorder are examined, as well as their interactions in producing either neurodevelopmental syndromes or schizophrenia itself. The implication of these findings for prevention and treatment are considered.

Common genetic vulnerability for nicotine and alcohol dependence in men

BACKGROUND

Nicotine and alcohol dependence often occur together. We examined data from male twin pairs to determine whether there are genetic or environmental influences common to nicotine and alcohol dependence, and, if so, to estimate the magnitude and correlation of these influences.

METHODS

Subjects were 3356 male-male twin-pair members of the Vietnam Era Twin Registry who participated in a 1992 telephone administration of the Diagnostic Interview Schedule Version 3 Revised. Genetic model fitting was performed to estimate the magnitude and correlation of genetic and environmental contributions to lifetime nicotine and alcohol dependence.

RESULTS

The heritability of nicotine dependence was 60.3% (95% confidence interval [CI], 55.4%-65.2%); that of alcohol dependence, 55.1% (95% CI, 49.7%-60.5%). The best-fitting model for the co-occurrence of lifetime nicotine and alcohol dependence included a substantial genetic correlation between both disorders (r = 0.68; 95% CI, 0.61-0.74) and a modest unique environmental correlation (r = 0.23; 95% CI, 0.14-0.32).

CONCLUSIONS

These data suggest a common genetic vulnerability to nicotine and alcohol dependence in men. This common genetic influence may partially explain the clinical and epidemiological observations that alcoholics are often dependent smokers.