title: Co-occurrence of IBS and symptoms of anxiety or depression, among Norwegian twins, is influenced by both heredity and intrauterine growth.
abstract: BACKGROUND
  Environmental and genetic factors contribute to variation in irritable bowel syndrome (IBS), anxiety and depression. Comorbidity between these disorders is high. A previous investigation of our population-based twin cohort revealed that low birth weight increased the risk for development of IBS, with environmental influences in utero as the most relevant contributing factor. We hypothesise that both intrauterine and genetic factors influence the co-occurrence of IBS and symptoms of anxiety and depression.
  
  
  METHODS
  A postal questionnaire sent to 12700 Norwegian twins born between 1967 and 1979 comprised a checklist of 31 illnesses and symptoms, including IBS and symptoms of anxiety and depression. The influence of genetic factors and intrauterine growth on comorbidity between these disorders were analysed in the full sample and compared to those based on only monozygotic (MZ) twin pairs discordant for IBS (95 pairs) in birth weight group < 2500 g and ≥ 2500 g.
  
  
  RESULTS
  In the co-twin analyses restricted growth (birth weight < 2500 g) was significantly associated with anxiety and depression (average birth weight difference of 181.0 g (p <0.0001) and 249.9 g (p < 0.0001), respectively). The analysis of the full sample revealed that IBS was significantly associated with symptoms of anxiety (adjusted OR = 2.5, 95% CI: 1.9, 3.3) and depression (adjusted OR = 2.3. 95% CI: 1.8, 3.0). Analyses of MZ pairs discordant for IBS indicated significant associations between IBS and symptoms of anxiety (OR = 3.7, 95% CI: 1.3, 10.5) and between IBS and symptoms of depression (OR = 4.2, 95% CI: 1.7, 9.9) only in the birth weight group below 2500 g.
  
  
  CONCLUSIONS
  Our findings suggest that genetic factors partly explain the association between IBS and symptoms of anxiety and depression. In the low range of birth weight (<2500 g), restricted fetal growth seems to be a common contributing factor to the co-occurrence between these disorders.
authors: Medical Department, Vestfold Hospital Trust, PO Box 2168, 3103, Tønsberg, Norway. maybente.bengtson@gmail.com.|EpiGen-Institute, Faculty Division Akershus University Hospital, University of Oslo, Oslo, Norway. maybente.bengtson@gmail.com.
authors: May-Bente
authors: MB
authors: Bengtson
authors: Norwegian University of Life Sciences, PO Box 5003, 1432, Ås, Norway. geir.aamodt@nmbu.no.
authors: Geir
authors: G
authors: Aamodt
authors: EpiGen-Institute, Faculty Division Akershus University Hospital, University of Oslo, Oslo, Norway. m.h.vatn@medisin.uio.no.
authors: Morten H
authors: MH
authors: Vatn
authors: Division of Epidemiology, The Norwegian Institute of Public Health, Oslo, Norway. Jennifer.Harris@fhi.no.
authors: Jennifer R
authors: JR
authors: Harris
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001007:Anxiety / Q000453:epidemiology* / Q000235:genetics*; D001724:Birth Weight; D016022:Case-Control Studies; D015897:Comorbidity; D003863:Depression / Q000453:epidemiology* / Q000235:genetics*; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology; D059647:Gene-Environment Interaction; D006306:Health Surveys; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000453:epidemiology* / Q000235:genetics*; D008297:Male; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D012893:Sleep Wake Disorders / Q000453:epidemiology; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D055815:Young Adult
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