title: Cryptorchidism concordance in monozygotic and dizygotic twin brothers, full brothers, and half-brothers.
abstract: OBJECTIVE
  To study concordance rates of cryptorchidism (undescended testis) in pairs of boys with varying family structure, to evaluate the risk contribution from the intrauterine environment and genetic factors.
  
  
  METHODS
  Population based study of 1,024,500 Danish boys born from January 1, 1973 to December 31, 2004. Classic twin method and computerized square dance design.
  
  
  METHODS
  Hospitals and outpatient clinics.
  
  
  METHODS
  Six groups of boy pairs: boys with no relation, paternal half-brothers, maternal half-brothers, full brothers, dizygotic twin brothers, and monozygotic twin brothers.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Status on each individual regarding cryptorchidism and orchiopexy from the Danish National Patient Register.
  
  
  RESULTS
  Concordance rates of cryptorchidism in the groups were as follows: boys with no relation 3.2% (95% confidence interval 2.7%-3.6%), paternal half-brothers 3.4% (2.3%-4.7%), maternal half-brothers 6.0% (4.5%-7.7%), full brothers 8.8% (8.3%-9.8%), dizygotic twin brothers 24.1% (16.0%-33.6%), and monozygotic twin brothers 27.3% (15.5%-41.2%).
  
  
  CONCLUSIONS
  The concordance rate was higher in maternal than in paternal half-brothers, and much higher but of equal magnitude in both twin groups. The findings strongly support that the intrauterine environment and maternal inheritance are contributing to the occurrence of cryptorchidism.
authors.affiliation: Department of Occupational Medicine, Aarhus University Hospital, Aarhus, Denmark. morten@sondergaard-jensen.dk
authors.forename: Morten Søndergaard
authors.initials: MS
authors.lastname: Jensen
authors.forename: Gunnar
authors.initials: G
authors.lastname: Toft
authors.forename: Ane Marie
authors.initials: AM
authors.lastname: Thulstrup
authors.forename: Tine Brink
authors.initials: TB
authors.lastname: Henriksen
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Bonde
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003456:Cryptorchidism / Q000235:genetics* / Q000601:surgery; D003718:Denmark; D004777:Environment; D020022:Genetic Predisposition to Disease; D040941:Heredity; D006801:Humans; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D056126:Orchiopexy; D010375:Pedigree; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult