Discordant retinoblastoma in monozygotic twins.
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.
Marcus
D M
DM
Department of Ophthalmology, Medical College of Georgia, Augusta 30912, USA.
Papastergiou
G I
GI
Patel
M
M
Pandya
A
A
Brooks
S E
SE
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