Monozygotic twins with discordant sexual phenotypes due to different ratios of mosaicism of 47,X,idic(Y),idic(Y)/46,X,idic(Y)/45,X

We report monozygotic twins of different sexual phenotypes. One of the twins had complete female external genitalia except for a mild clitoromegaly. She had bilateral gonads consisting of the wavy stroma and scant dysgenetic seminiferous tubules. No androgen secretion was induced by gonadotrophin stimulation. The other twin had hypospadiac male genitalia. His gonads were located intrascrotally and he had good androgenic response to a stimulation test. Conventional and fluorescence in situ hybridization chromosome analysis disclosed that both twins had a 47,X,idic(Y),idic(Y)/46,X,idic(Y)/45,X and 47,X, + mar x 2.ish idic(Y)(q11.2)(DYZ3 ++ x 2)/46,X, + mar.ish idic(Y)(q11.2)(DZY3 ++)/45,X. These twins were clinically monochorionic and allelotype analysis in these twins and their parents with microsatellite markers showed the affirmative probability of 0.999999994 for monozygosity. The ratio of mosaicism, gonadal histology, and testosterone productivity were reasonably correlated to the genital virilization in these monozygotic twins, showing discordant sexual phenotypes.