title: Identification and validation of mixed anxiety-depression.
abstract: BACKGROUND
  Mixed anxiety-depression (MAD) has been under scrutiny to determine its potential place in psychiatric nosology. The current study sought to investigate its prevalence, clinical characteristics, course and potential validators.
  
  
  METHODS
  Restricted latent-class analyses were fit to 12-month self-reports of depression and anxiety symptom criteria in a large population-based sample of twins. Classes were examined across an array of relevant indicators (demographics, co-morbidity, adverse life events, clinical significance and twin concordance). Longitudinal analyses investigated the stability of, and transitions between, these classes for two time periods approximately 1.5 years apart.
  
  
  RESULTS
  In all analyses, a class exhibiting levels of MAD symptomatology distinctly above the unaffected subjects yet having low prevalence of either major depression (MD) or generalized anxiety disorder (GAD) was identified. A restricted four-class model, constraining two classes to have no prior disorder history to distinguish residual or recurrent symptoms from new onsets in the last year, provided an interpretable classification: two groups with no prior history that were unaffected or had MAD and two with prior history having relatively low or high symptom levels. Prevalence of MAD was substantial (9-11%), and subjects with MAD differed quantitatively but not qualitatively from those with lifetime MD or GAD across the clinical validators examined.
  
  
  CONCLUSIONS
  Our findings suggest that MAD is a commonly occurring, identifiable syndromal subtype that warrants further study and consideration for inclusion in future nosologic systems.
authors.affiliation: Department of Psychiatry,Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA 23298-0126,USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Hettema
authors.affiliation: Department of Psychiatry,Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA 23298-0126,USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Aggen
authors.affiliation: Department of Psychiatry,Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA 23298-0126,USA.
authors.forename: T S
authors.initials: TS
authors.lastname: Kubarych
authors.affiliation: Department of Psychiatry,Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA 23298-0126,USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Neale
authors.affiliation: Department of Psychiatry,Virginia Institute for Psychiatric and Behavioral Genetics,Virginia Commonwealth University,Richmond,VA 23298-0126,USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Kendler
mesh_terms: D000328:Adult; D001007:Anxiety; D001008:Anxiety Disorders / Q000453:epidemiology*; D015897:Comorbidity; D003863:Depression; D003865:Major Depressive Disorder / Q000453:epidemiology*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D011569:Psychiatric Status Rating Scales; D011570:Psychiatry / Q000145:classification*; D014427:Twins / Q000523:psychology*; D055815:Young Adult
keywords: Anxiety; depression; twin studies