General Medical Information

Gonads

Joe Leigh Simpson

In most 45,X adults with gonadal dysgenesis, the normal gonad is replaced by a white fibrous streak, 2 to 3 cm long and about 0.5 cm wide, located in the position ordinarily occupied by the ovary. A streak gonad is characterized histologically by interlacing waves of dense fibrous stroma, indistinguishable from normal ovarian stroma. That germ cells usually are completely absent in adults but present in 45,X embryos is the basis for the belief that the pathogenesis of germ cell failure is increased atresia, not failure of germ cell formation. Ovarian rete tubules, which probably originate from either mesonephric tubules or medullary sex cords, are present in the medial portion of most streak gonads. Hilar cells usually are detected in streak gonads of patients past the age of expected puberty.

That 45,X humans manifest streak gonads is not as obvious as one might expect, with relatively normal ovarian development occurring in many other monosomy X mammals (e.g., mice). The more likely explanation is that, in humans, not all loci on the normal heterochromatic (inactive) X are inactivated. In addition, X-inactivation never exists in oocytes; X-reactivation of germ cells occurs before entry in meiotic oogenesis. X-inactivation also can occur only after some crucial time of differentiation, beyond which only a single euchromatic (active) X is necessary for continued oogenesis.