MONOZYGOTIC (MZ) TWINS DISCORDANT FOR SEX

Abstract

A pair of adolescent twins, discordant for sex, was identified as MZ on the basis of concordance for 22 blood groups and other biochemical markers. The proband has short stature, webbed neck, malformed left kidney, high plasma gonadotropins and other features of Turner's syndrome. Cytogenetic studies revealed a 46XY chromosome complement in peripheral blood, 46XY/45X in skin fibroblasts and 45X in fibroblasts cultured from streak gonads. Her MZ normal appearing male twin has a 46XY karyotype. The dermatoglyphics are similar in both twins but the total ridge count is higher in the girl. A review of the literature reveals 3 other reports of MZ twins discordant for sex. In one pair there was a phenotypically normal male with a 46XY karyotype, and the female twin had a 45X karyotype and findings of Turner's syndrome. In the second pair the male, although phenotypically normal, showed a 45X karyotype while the female twin showed 45X/46XY mosaicism with features consistent with mixed gonadal dysgenesis. Both members of the third twin pair showed findings characteristic of mixed gonadal dysgenesis. The male twin had a 45X/46XY chromosome complement and the female, with findings more suggestive of Turner's syndrome, had a 45X chromosome pattern. The concurrence of gonadal dysgenesis and MZ twinning may shed light on embryonic gonadal development and pathogenesis of the various types of gonadal dysgenesis.