Twin–twin confusion syndrome: Blood chimerism in opposite sex dizygotic twins

Sex‐discordant monochorionic twins with blood and tissue chimerism

“…). This pattern of microsatellites markers has been demonstrated in blood samples of other MC/DZ twins [Aoki et al, ; Walker et al, ; Hawcutt et al, ]. The boy's blood aCGH+SNP analysis demonstrated five track SNP combinations (AAAA, AAAB, AABB, ABBB, and BBBB) suggesting the presence of two different genomes, which supports the presence of chimerism (Fig.…”

“…Although placental pathology reports are not consistent in all the studies, they have documented blood vessel collaterals that explained, in part, why the chimerism can be confined to the blood. This mechanism does not seem to be plausible in our case, since the male has a combination of cell lines in the blood and in the skin [Quintero et al, ; Souter et al, ; Williams et al, ; Aoki et al, ; Walker et al, ; Ekelund et al, ; Hackmon et al, ; Hawcutt et al, ; Chen et al, ; Kanda et al, ]. In true sex‐discordant MC/DZ twins with confined‐blood chimerism, the male's skin is only 46,XY, the female's is only 46,XX, and the blood of both should show a combination of 46,XY and 46,XX, reflecting the placental blood sharing.…”

“…Monochorionic (MC) twins are expected to be genetically and phenotypically identical since they arise during the early cleavage of a single embryo. This notion was challenged by reports of sex‐discordant MC/DZ twins, demonstrating that dizygotic twins (DZ) can also be monochorionic [Quintero et al, ; Souter et al, ; Williams et al, ; Ginsberg et al, ; Aoki et al, ; Souter et al, ; Walker et al, ; Ekelund et al, ; Hackmon et al, ; Hawcutt et al, ; Chen et al, ; Kanda et al, ]. This finding provided an explanation for the observed discordant phenotype seen in some cases of MC twins [Bourthoumieu et al, ; Charles, ; Malan et al, ]…”

“…This has been referred to as “confined‐blood chimerism.” This is relatively common compared to solid tissue chimerism, which to our knowledge, has only been demonstrated in two reports [Ginsberg et al, ; Souter et al, ]. Most of the reported cases are associated with the use of assisted reproductive technology (ART), but this might represent ascertainment bias [Quintero et al, ; Souter et al, ; Williams et al, ; Ginsberg et al, ; Aoki et al, ; Souter et al, ; Walker et al, ; Ekelund et al, ; Hawcutt et al, ; Chen et al, ; Kanda et al, ].…”