McCune-Albright syndrome in a discordant monozygotic twin.

Background: McCune-Albright syndrome is a sporadic disorder characterized by polystotic fibrous dysplasia, pigmented patches of skin, and endocrinological abnormalities.

Objectives: To compare the genetic characteristics of the GNAS1 gene in a monozygotic pair of twins, one of whom was diagnosed with MAS while the other had no indication of the syndrome.

Methods: We performed a molecular analysis of the GNAS1 gene in DNA extracted from peripheral blood cells and quantification of mRNA extracted from lymphoblastoid cells from both twins by quantitative real-time polymerase chain reaction.

Results: Monozygosity of the twins was confirmed by typing them to four highly polymorphic microsatellites. Molecular analysis of the GNAS1 gene extracted from both twins did not reveal the cause of this discordance.

Conclusions: It is possible that the exact molecular mechanism for the MAS discordance can only be determined by sampling affected tissues.