title: Fetal blood sampling demonstrating chimerism in monozygotic twins discordant for sex and tissue karyotype (46,XY and 45,X)
abstract: Fetal blood sampling has been used in the genetic work-up of twin gestations for rapid karyotyping. We present a case of twins which on ultrasound evaluation revealed hydrops fetalis in one twin and a normal second twin. Fetal blood sampling revealed the presence of mosaicism for 46,XY/45,X in both twins. HLA antigen testing showed the twins to be identical. The patient elected pregnancy termination. Blood chromosomal analysis after delivery revealed both twins to have 46,XY/45,X mosaicism, but the twin with signs of hydrops fetalis had tissue chromosomes of 45,X and the normal twin had tissue chromosomes of 46,XY. Amniotic fluid chromosomal analysis revealed 46,XY in twin A and 45,X in twin B. This represents a case of identical (monozygotic) twins with sex discordance. In this case, there was the probable occurrence of post-zygotic chromosomal non-disjunction leading to the discordancy of the sex in this set of twins. With the presence of vascular communication in monozygotic twins, there is the possibility of exchange of blood in monozygotic twins and the result of blood chimerism in twins.
authors.affiliation: Department of Obstetrics and Gynecology, Baylor College of Medicine, Houston, TX 77030.
authors.forename: W
authors.initials: W
authors.lastname: Gonsoulin
authors.forename: K L
authors.initials: KL
authors.lastname: Copeland
authors.forename: R J
authors.initials: RJ
authors.lastname: Carpenter
authors.forename: M R
authors.initials: MR
authors.lastname: Hughes
authors.forename: F F
authors.initials: FF
authors.lastname: Elder
mesh_terms: D000328:Adult; D002678:Chimera / Q000235:genetics*; D005260:Female; D005312:Fetal Blood / Q000032:analysis*; D006801:Humans; D007621:Karyotyping; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012729:Sex Chromosome Aberrations / Q000175:diagnosis*; D014427:Twins / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*