title: Evidence for genetic influences common and specific to symptoms of generalized anxiety and panic.
abstract: BACKGROUND
  Generalized anxiety disorder (GAD) and panic disorder (PD) often co-occur and have been shown to be heritable. Researchers have debated the validity of the distinction between GAD and PD. To test for distinction between disorders, we estimated the genetic and environmental contributions which were specific and common to GAD and PD in a cohort of male-male twin pairs.
  
  
  METHODS
  Data were obtained from a telephone interview performed in 1992 utilizing the Diagnostic Interview Schedule Version 3-Revised. Interviews were administered to 6724 male-male monozygotic and dizygotic twin pair members of the Vietnam Era Twin Registry. We defined lifetime GAD by the report of six or more DSM-III-R symptoms and lifetime PD by the report of four or more DSM-III-R symptoms.
  
  
  RESULTS
  The lifetime co-occurrence of GAD and PD was best explained by a model which did not include family environmental influences. The variance in risk for GAD was due to a 37.9% influence from additive genetic factors with the remainder due to unique environmental influences. The variance in risk for PD was due to a 22.6% additive genetic contribution which was common with GAD and a 21.2% non-additive genetic contribution specific to PD with the remainder of variance in risk for PD due to unique environmental influences.
  
  
  CONCLUSIONS
  Results may be limited to middle aged males. Model fitting with full diagnostic criteria was not possible due to low prevalences.
  
  
  CONCLUSIONS
  Our data suggest a distinction in liability for GAD versus PD. The common genetic influence to GAD and PD may partially account for the risk of the co-occurrence of these disorders in a lifetime.
authors.affiliation: School of Public Health, St. Louis University Health Sciences Center, St. Louis, MO, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Scherrer
authors.forename: W R
authors.initials: WR
authors.lastname: True
authors.forename: H
authors.initials: H
authors.lastname: Xian
authors.forename: M J
authors.initials: MJ
authors.lastname: Lyons
authors.forename: S A
authors.initials: SA
authors.lastname: Eisen
authors.forename: J
authors.initials: J
authors.lastname: Goldberg
authors.forename: N
authors.initials: N
authors.lastname: Lin
authors.forename: M T
authors.initials: MT
authors.lastname: Tsuang
mesh_terms: D017668:Age of Onset; D001008:Anxiety Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D003937:Diagnosis, Differential; D004200:Diseases in Twins; D004777:Environment; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D016584:Panic Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D015995:Prevalence; D011569:Psychiatric Status Rating Scales; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D013313:Stress Disorders, Post-Traumatic / Q000523:psychology; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology; D014744:Vietnam; D014857:Warfare