title: Genetic and environmental contributions to the overlap between psychological, fatigue and somatic symptoms: a twin study in Sri Lanka.
abstract: BACKGROUND
  Somatic symptoms often co-occur with psychological symptoms but this overlap is poorly understood. Some aspects of this overlap differ in the South Asian context, but it is not clear whether this is a reporting effect or an underlying difference in experienced illness.
  
  
  METHODS
  Home interviews were administered to 4,024 twins randomly selected from a population-based twin register in the Colombo district of Sri Lanka (the CoTASS study). These included assessments of psychological, somatic and fatigue symptoms. The data were analyzed using factor analytic and quantitative genetic approaches.
  
  
  RESULTS
  Confirmatory factor analysis showed that the symptoms from the three scales represented three separate dimensions, rather than all tapping into a single dimension. However, familial correlations among the data were most consistent with a common pathway model. This implies that a portion of the underlying vulnerability is common across psychological, fatigue and somatic symptoms. There were sex differences in the etiology of this model, with shared environmental and genetic influences playing different roles in men and women.
  
  
  CONCLUSIONS
  There is a complex etiological relationship between psychological, fatigue and somatic symptoms. This is similar in Sri Lanka to Western countries, but there may be a greater influence from the family environment, suggesting that care needs to be taken when generalizing research findings between countries. People who complain of certain fatigue or somatic symptoms may well also have psychological symptoms, or may have genetic or environmental vulnerabilities to such problems.
authors.affiliation: MRC Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, United Kingdom. harriet.ball@kcl.ac.uk
authors.forename: Harriet A
authors.initials: HA
authors.lastname: Ball
authors.forename: Sisira H
authors.initials: SH
authors.lastname: Siribaddana
authors.forename: Athula
authors.initials: A
authors.lastname: Sumathipala
authors.forename: Yulia
authors.initials: Y
authors.lastname: Kovas
authors.forename: Nick
authors.initials: N
authors.lastname: Glozier
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
authors.forename: Peter
authors.initials: P
authors.lastname: McGuffin
authors.forename: Matthew
authors.initials: M
authors.lastname: Hotopf
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004200:Diseases in Twins / Q000175:diagnosis / Q000235:genetics / Q000523:psychology; D005221:Fatigue / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D010641:Phenotype; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors; D013188:Sri Lanka / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014429:Twins, Dizygotic / Q000235:genetics* / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics* / Q000523:psychology; D055815:Young Adult