title: Chronic fatigue and anxiety/depression: a twin study.
abstract: BACKGROUND
  Up to three-quarters of patients with fatigue syndromes have comorbid mood or anxiety disorders, suggesting that chronic fatigue is a forme fruste of anxiety or depressive states.
  
  
  OBJECTIVE
  To establish whether the association of chronic fatigue with psychological distress is causal or due to a common genetic or environmental factor.
  
  
  METHODS
  69 monozygotic (MZ) and 31 dizygotic (DZ) female twin pairs, with only one co-twin reporting at least 6 months of fatigue, completed questions on fatigue, the General Health Questionnaire (GHQ) and a structured psychiatric interview. We examined the effects of three progressively more stringent definitions of chronic fatigue on four GHQ sub-scales.
  
  
  RESULTS
  Fatigued MZ and DZ twins by all definitions were significantly more depressed, anxious, somatically preoccupied and socially dysfunctional than their non-fatigued co-twins. Intrapair differences were similar in DZ and MZ twins, but non-significant differences were observed for the somatic symptoms and anxiety/insomnia sub-scales.
  
  
  CONCLUSIONS
  In this sample, chronic fatigue and psychological distress are strongly associated without evidence for genetic covariation, implying that the association is environmental, or due to overlapping definitions. Any genetic covariation missed is likely to involve anxiety rather than depression.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98104, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Roy-Byrne
authors.forename: Niloofar
authors.initials: N
authors.lastname: Afari
authors.forename: Suzanne
authors.initials: S
authors.lastname: Ashton
authors.forename: Mary
authors.initials: M
authors.lastname: Fischer
authors.forename: Jack
authors.initials: J
authors.lastname: Goldberg
authors.forename: Dedra
authors.initials: D
authors.lastname: Buchwald
mesh_terms: D000328:Adult; D001008:Anxiety Disorders / Q000150:complications* / Q000235:genetics; D003866:Depressive Disorder / Q000150:complications* / Q000235:genetics; D004200:Diseases in Twins; D015673:Fatigue Syndrome, Chronic / Q000150:complications* / Q000175:diagnosis / Q000235:genetics; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008875:Middle Aged; D011795:Surveys and Questionnaires; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic