Monochorionic twins with the same blood karyotype of 46,XY/47,XYY but different phenotypes

Abstract

We report the case of a 13-year-old woman who was pregnant with phenotypically discordant monochorionic twins: one with cystic hygroma and hydrops, the other one normal. Fetal blood sampling was performed by intrahepatic blood collection for karyotyping of both fetuses, revealing the same genotype of 46,XY/47,XYY in 2:1 proportion. Phenotypic discordance in monozygotic twins can have various causes, such as placental vascular anatomy, differences in allocation of the number of blastomeres or genetic postzygotic events.

Monozygotic twins discordant for trisomy 18

“…Discordance in monozygous twins has been described for trisomy 212–4 and trisomy 135. Discordances in the sex chromosomes are more commonly reported: 46,XX with 45,X6, 46,XY with 45,X7–12, 47,XYY with 45,X13, 47,XYY with 46,XY14 and a 47,XXY zygote resulting in 46,XX and 46,XY offspring15. However, this is the first report on discordance for trisomy 18.…”