Gonadal Dysgenesis and Its Unilateral Variant with Testis in Monozygous Twins: Related to Discordance in Sex Chromosomal Status

Abstract

These twins of carefully established monozygosity both displayed classic stigmata of the Turner syndrome, but with probably closely related discordance between clinical, gonadal and cytogenetic components. Although clitoridal hypertrophy was an additional feature in each, it was of only slight degree in Twin I, yet penile with hooded prepuce in Twin II, in whom it was found to be associated with a testis opposite to unilateral “gonadal streak.” In Twin I, “streaks” were bilateral, and an XO/45 constitution was denned in different tissues. In Twin II, however, extensive exploration of blood, skin, fallopian tube, testis and streak exposed the Ychromosome in somatic and gonosomic mosaicism of XO/XY type, although XY cells were sparse (2–18%). Therefore, these twins represent a significant illustration of the transition between classic gonadal dysgenesis of 45/XO constitution and more advanced male intersexuality, presumably stemming from the XO/XY mosaicism. The chromosomal situation and discordance may be accounted for by twinning after a mitotic error such as anaphase lag of Y and separation of blastomeres XO and XY occurring relatively late. This concept is supported by evidence of lateral inversion especially in gonado-urinary components, with even a “double uretic” anomaly emerging on opposite sides.