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Anxiety disorders and major depressive disorder (MDD) are among the most common mental disorders in the United States,[1] with high individual and societal burden derived from their considerable associated work and social impairment.[2,3] Decreasing the burden of anxiety disorders and MDD is an important public health priority. Anxiety disorders often co-occur with each other and with MDD[4,5] suggesting the existence of a latent structure that may parsimoniously explain these patterns of comorbidity[6–9]. Several studies have examined the genetic liability of anxiety disorders and MDD, and consistently concluded that most of this genetic liability is exerted at the level of the latent variable,[8, 10–13] rather than at the disorder-specific level. Because anxiety disorders and MDD share a broad range of other risk factors,[14–24] an essential step in the development of more effective treatment and prevention interventions is to determine whether those factors exert their effect through the common latent variable, directly on each disorder, or through a combination of effects at both levels.[14, 16, 25] We sought tsreo address this gap in knowledge by drawing on data from a large, nationally representative survey to compare the common and the specific contribution of a set of observable risk factors to risk of anxiety disorders and MDD. We followed a conceptual model of risk factors, which was initially developed by Kendler and colleagues to examine the prevalence of MDD,[26, 27] but seems to be applicable to other internalizing disorders.[28] Because anxiety disorders often co-occur with each other and with MDD and seem to have a partially shared liability,[8, 13, 14] prior to our analyses, we hypothesized that the comorbidity structure of anxiety disorders and MDD would be well described by a single latent variable and that the risk factors postulated in Kendler’s model would exert part of their effect through this latent variable. However, because the prevalence and course of the different anxiety disorder and MDD does not fully overlap[29–31] and they also have nonshared variance, we also hypothesized that the risk factors would also partially exert their effect directly on the individual disorders.

Generalized anxiety disorder (GAD) and major depressive disorder (MDD) are highly prevalent, disabling conditions associated with considerable personal and societal burden.(1) Because MDD and GAD have high symptom overlap(2) and often co-occur,(3) there is considerable controversy regarding their separation as distinct diagnostic entities. Some studies and meta-analyses have suggested that MDD and several anxiety disorders have a modest familial aggregation and moderate levels of cross heritability,(4) but other studies have found mixed evidence for shared familial risk.(5) Other studies have found distinguishable patterns of comorbidity between GAD and MDD,(6) although whether co-occurrence of MDD and GAD has any influence on these differences is unknown. Several twin studies have also examined the relationship between MDD and GAD in large population samples.(7) The Virginia Adult Twin Study of Psychiatric and Substance Use Disorders (VATSPSUD) found that the correlation for environmental risk factors between MDD and GAD was 0.51, indicating that environmental risk factors for these disorders are moderately correlated. The VATSPSUD estimated the genetic correlation between MDD and GAD to be 1, indicating a very strong relationship between the genetic risk factors for both disorders.(7) Data from the Australian and Dutch Twins and Siblings Study also suggest considerable overlap in genetic risk factors for GAD and MDD,(8) and data from the Swedish Twin Registry(9) indicate that GAD and MDD share the same genetic factors but their environmental determinants are mostly distinct. Three large prospective epidemiological studies have also indicated that the developmental risk factors for GAD and MDD do not fully overlap,(10-12) suggesting that despite their similarities, the etiological pathways of these two disorders may differ. Application of latent variable techniques to three large community surveys in which psychiatric diagnoses were used as indicators have suggested that MDD and GAD may be part of an underlying factor named “anxious misery”,(13-16) but other studies have found divergent results.(17) In addition, a recent meta-analysis of the relationship between anxiety sensitivity and internalizing disorders found that anxiety sensitivity is more strongly correlated with agoraphobia, GAD and posttraumatic stress than with depression, raising new questions regarding the relationship between GAD and MDD.(18) The present study seeks to build on existing knowledge by examining data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), a large, nationally representative sample of US adults. The specific goals of our study were: 1) to compare the sociodemographic characteristics and comorbidity patterns of individuals with GAD, MDD, and those with both disorders (GAD-MDD); and, 2) to determine the factor structure of the individual DSM-IV criteria for GAD and MDD.

Background: Burden related to major depressive disorder (MDD) derives mostly from long-term occurrence of symptoms. This study aims to examine the prevalence, sociodemographic correlates, patterns of 12-month and lifetime psychiatric comorbidity, lifetime risk factors, psychosocial functioning, and mental health service utilization of chronic major depressive disorder (CMDD) compared to nonchronic major depressive disorder. Methods: Face-to-face interviews were conducted in the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (n = 43,093). Results: The 12-month and lifetime prevalence of CMDD within the population meeting criteria for MDD was 26.5% and 24.0%, respectively. Individuals reporting a chronic course of MDD were socioeconomically and educationally disadvantaged, tended to be older, report loss of spouse or history of divorce, live in rural areas, have public assistance, low self-esteem, worse overall health and more likely to report comorbidities, most importantly dysthymia, generalized anxiety disorder, avoidant, and dependant personality disorder. Individuals with chronic MDD were more likely to report familial but not childhood onset risk factors for MDD. Those suffering CMDD were more likely to seek and receive mental health care than other forms of MDD, even though it took longer to start treatment. Conclusion: Chronic course of MDD is related to still worse socioeconomic conditions, educational achievement, more comorbidities, and family risk factors, although other courses of MDD carried greater risk of unmet treatment. Depression and Anxiety, 2011. © 2011 Wiley-Liss, Inc. Language: en