title: Discordant retinoblastoma in monozygotic twins.
abstract: OBJECTIVE
  We report cases of discordant retinoblastoma in twins confirmed to be monozygotic by DNA analysis.
  
  
  METHODS
  Twin A demonstrated severe, bilateral, multifocal retinoblastoma, which was recalcitrant to external beam irradiation and chemoreduction. Twin B has not demonstrated retinoblastoma. DNA analysis was performed with polymorphic microsatellite markers to confirm monozygosity. Single-stranded conformation polymorphism and Southern blot analysis of the retinoblastoma gene were performed.
  
  
  RESULTS
  Molecular genetic analyses confirmed monozygosity but failed to disclose a retinoblastoma gene mutation in either twin.
  
  
  CONCLUSIONS
  The extreme phenotypic discordance may best be explained by an unidentified, postzygotic retinoblastoma gene mutation in early embryonic development of the affected twin.
authors.affiliation: Department of Ophthalmology, Medical College of Georgia, Augusta 30912, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Marcus
authors.forename: G I
authors.initials: GI
authors.lastname: Papastergiou
authors.forename: M
authors.initials: M
authors.lastname: Patel
authors.forename: A
authors.initials: A
authors.lastname: Pandya
authors.forename: S E
authors.initials: SE
authors.lastname: Brooks
mesh_terms: D015139:Blotting, Southern; D002675:Child, Preschool; D004200:Diseases in Twins; D006801:Humans; D018807:Polymorphism, Single-Stranded Conformational; D019572:Retinal Neoplasms / Q000235:genetics* / Q000473:pathology; D012175:Retinoblastoma / Q000235:genetics* / Q000473:pathology; D014430:Twins, Monozygotic