title: Practical considerations on the use of extreme sib-pairs for obesity.
abstract: OBJECTIVE
  The extreme sib-pair approach has been shown to be a powerful strategy to identify susceptibility loci linked to quantitative traits. The body mass index is the usually assessed trait in genetic studies on human obesity. Environmental factors clearly play an important role for this trait. We hypothesized that the low weight of most sibs who were seemingly discordant to the obese index proband was influenced by other environmental and/or genetic factors like restrained eating or psychiatric disorders.
  
  
  METHODS
  A screening questionnaire was sent to parents of all consecutively admitted patients three weeks prior to referral of index probands for inpatient treatment of obesity. The first 320 families were further investigated. Twenty-seven seemingly extremely discordant sib-pairs (ED) were identified and examined in detail.
  
  
  RESULTS
  The low weight of most sibs who were seemingly discordant to the obese index proband was influenced by factors like restrained eating or psychiatric disorders. Only 20% of the interviewed ED could be considered as genuine ED.
  
  
  CONCLUSIONS
  We conclude that extensive medical evaluation is necessary if the aim is to guarantee genuine ED in family studies for human obesity. Non-paternity deserves specific attention in ED studies.
authors.affiliation: Institut für Medizinische Biometrie und Statistik, Universität zu Lübeck, 23538 Lübeck, Germany. ziegler@imbs.uni-luebeck.de
authors.forename: A
authors.initials: A
authors.lastname: Ziegler
authors.forename: N
authors.initials: N
authors.lastname: Barth
authors.forename: H
authors.initials: H
authors.lastname: Coners
authors.forename: H
authors.initials: H
authors.lastname: Mayer
authors.forename: J
authors.initials: J
authors.lastname: Hebebrand
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D002648:Child; D015986:Confounding Factors, Epidemiologic; D005247:Feeding Behavior; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008297:Male; D008403:Mass Screening; D009765:Obesity / Q000453:epidemiology / Q000235:genetics* / Q000628:therapy; D040641:Quantitative Trait Loci; D018570:Risk Assessment; D012307:Risk Factors; D035781:Siblings; D012931:Social Environment; D011795:Surveys and Questionnaires