title: Discordant retinoblastoma in monozygotic twins due to deletion of 13q14.
abstract: OBJECTIVE
  To report discordant retinoblastoma in monozygotic twins, confirmed by GeneScan.
  
  
  METHODS
  One twin presented unilateral retinoblastoma that was treated with enucleation; the other twin had no retinoblastoma. To confirm monozygosity, DNA from leukocytes was analyzed through GeneScan with highly polymorphic markers; to exclude 13q14 deletion, FISH analysis was performed in leukocytes and oral cells of both twins and their parents and in retinal tissue of the affected twin with the cDNA LSI RB1 probe.
  
  
  RESULTS
  GeneScan analysis confirmed monozygosity. 13q14 deletion was observed in homozygous state in retinal tissue and in heterozygous state in oral cells and leukocytes of the affected twin. The nonaffected twin and parents showed no deletion of 13q14.
  
  
  CONCLUSIONS
  These data show unexpected differences in monozygotic twins that could be explained by postzygotic events in embryonic development.
authors.affiliation: Ophthalmology Department, General Hospital of Mexico, Mexico, D.F. - Mexico.
authors.forename: Olga M
authors.initials: OM
authors.lastname: Messina-Baas
authors.forename: María Estela
authors.initials: ME
authors.lastname: Arroyo-Yllanes
authors.forename: J Fernando
authors.initials: JF
authors.lastname: Pérez-Pérez
authors.forename: Luz María
authors.initials: LM
authors.lastname: González-Huerta
authors.forename: Sergio Alberto
authors.initials: SA
authors.lastname: Cuevas-Covarrubias
mesh_terms: D002872:Chromosome Deletion; D002882:Chromosomes, Human, Pair 13 / Q000235:genetics*; D004200:Diseases in Twins / Q000235:genetics*; D015353:Eye Enucleation; D005260:Female; D006579:Heterozygote; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007223:Infant; D019572:Retinal Neoplasms / Q000235:genetics*; D012175:Retinoblastoma / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*