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Discordant retinoblastoma in monozygotic twins
D M Marcus1, G I Papastergiou, M Patel
1Department of Ophthalmology, Medical College of Georgia, Augusta 30912, USA.
Purpose:
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.