Molecular studies of parental origin and mosaicism in 45,X conceptuses.

The present report summarizes molecular studies of parental origin and sex chromosome mosaicism in forty-one 45,X conceptuses, consisting of 29 spontaneous abortions and 12 liveborn individuals with Turner syndrome. Our studies indicate that most 45,X conceptuses have a single, maternally derived X chromosome, regardless of whether the conceptus is liveborn or spontaneously aborted. In studies of mosaicism, our identification of X- and Y-chromosome mosaics among 45,X spontaneous abortions indicates that mosaicism does not ensure survival to term of 45,X fetuses. However, the incidence of sex chromosome mosaicism is substantially higher in liveborn than in aborted 45,X conceptuses, indicating that the presence of a second cell line increases the likelihood of survival to term.