title: Hypospadias is related to birth weight in discordant monozygotic twins.
abstract: OBJECTIVE
  Hypospadias is a common urogenital malformation in boys. The etiology is unknown but genetic and environmental factors are involved. Because monozygotic twins have the same genetic constitution, we studied disease discordant twin pairs to evaluate environmental risk factors while controlling for genetic effects.
  
  
  METHODS
  We used questionnaires to identify 28 male twins discordant for hypospadias at 4 pediatric surgical clinics in Sweden. Using deoxyribonucleic acid fingerprinting, and histopathological examination of the placenta and fetal membranes 18 twin pairs were diagnosed as monozygotic.
  
  
  RESULTS
  In 16 of the 18 monozygotic pairs discordant for hypospadias the twin with the lowest birth weight has hypospadias. Mean difference in birth weight was 498 gm. (t = 3.8, p <0.01).
  
  
  CONCLUSIONS
  Environmental factors associated with low birth weight are involved in the etiology of hypospadias.
authors.affiliation: Department of Molecular Medicine, Karolinska Hospital, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Fredell
authors.forename: P
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: N L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: J
authors.initials: J
authors.lastname: Svensson
authors.forename: A
authors.initials: A
authors.lastname: Nordenskjöld
mesh_terms: D001724:Birth Weight; D006801:Humans; D007021:Hypospadias / Q000453:epidemiology*; D008297:Male; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014430:Twins, Monozygotic