title: Anorexia and bulimia nervosa in same-sex and opposite-sex twins: lack of association with twin type in a nationwide study of Finnish twins.
abstract: OBJECTIVE
  The authors tested the hypothesis that either prenatal feminization or masculinization hormone influences in utero or later socialization affects the risk for anorexia and bulimia nervosa and disordered eating in members of opposite-sex twin pairs.
  
  
  METHODS
  Finnish twins (N=2,426 women, N=1,962 men with known zygosity) from birth cohorts born 1974-1979 were assessed at age 22 to 28 years with a questionnaire for eating disorder symptoms. Based on the questionnaire screen, women (N=292), men (N=53), and their cotwins were interviewed to assess diagnoses of anorexia nervosa and bulimia nervosa (per DSM-IV and broad criteria).
  
  
  RESULTS
  In women from opposite-sex twin pairs, the prevalence of DSM-IV or broad anorexia nervosa was not significantly different than that of women from monozygotic pairs or same-sex dizygotic pairs. Of the five male anorexia nervosa probands, only one was from an opposite-sex twin pair. Bulimia nervosa in men was too rare to be assessed by zygosity; the prevalence of DSM-IV or broad bulimia nervosa did not differ in women from opposite- versus same-sex twin pairs. In both sexes, the overall profile of indicators on eating disorders was rather similar between individuals from opposite- and same-sex pairs.
  
  
  CONCLUSIONS
  The authors found little evidence that the risk for anorexia nervosa, bulimia nervosa, or disordered eating was associated with zygosity or sex composition of twin pairs, thus making it unlikely that in utero femininization or masculinization or socialization effects of growing up with an opposite-sex twin have a major influence on the later development of eating disorders.
authors.affiliation: Columbia University, New York State Psychiatric Institute, 1051 Riverside Dr., Unit 23, New York, NY 10032, USA. anu.raevuori@helsinki.fi
authors.forename: Anu
authors.initials: A
authors.lastname: Raevuori
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Hans W
authors.initials: HW
authors.lastname: Hoek
authors.forename: Elina
authors.initials: E
authors.lastname: Sihvola
authors.forename: Aila
authors.initials: A
authors.lastname: Rissanen
authors.forename: Anna
authors.initials: A
authors.lastname: Keski-Rahkonen
mesh_terms: D000293:Adolescent; D000328:Adult; D000856:Anorexia Nervosa / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D052018:Bulimia Nervosa / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D010641:Phenotype; D015995:Prevalence; D011795:Surveys and Questionnaires; D014427:Twins / Q000235:genetics*