Chimerism of Buccal Membrane Cells in a Monochorionic Dizygotic Twin

Abstract

No monochorionic dizygotic twins (MCDZTs) with cellular chimerism involving cells other than blood cells have been reported in the literature to date. Here we report a probable first case of MCDZTs with buccal cell chimerism. A 32-year-old woman conceived twins by in vitro fertilization by using 2 cryopreserved blastocysts that were transferred into her uterus. An ultrasound scan at 8 weeks’ gestation showed signs indicative of monochorionic twins. A healthy boy and a healthy girl were born, showing no sexual ambiguity. Cytogenetic analyses and microsatellite studies demonstrated chimerism in blood cells of both twins. Notably, repeated fluorescence in situ hybridization and microsatellite studies revealed chimerism in buccal cells obtained from 1 of the twins. Although the mechanism through which buccal cell chimerism was generated remains to be elucidated, ectopic differentiation of chimeric hematopoietic cells that migrated to the buccal membrane or the cellular transfer between the 2 embryos at the early stage of development might be responsible for the phenomenon. This hypothesis raises an interesting issue regarding embryonic development and cellular differentiation into organs during fetal development. Given the possibility of cryptic chimerism in various organs including gonadal tissues in MCDZTs, close observation will be required to determine whether complications develop in the course of the patients’ growth.

Quantitation of the cellular content of saliva and buccal swab samples

“…Therefore, genotype may vary in both saliva and buccal swabs following bone marrow allografts. A similar problem involving chimerism has been seen in fraternal twins that have shared the same placenta, an uncommon, but not rare occurrence 15 , 16 . More common reasons for knowing cellular content is for studies of epigenomics 9 , 17 – 19 , gene expression 20 , 21 and proteomics 2 , in which the levels of analytes originate from mixed cell types, confounding case-control analysis.…”

“…Taken together, these results suggest that buccal swabs are preferable to saliva for maximising epithelial cell content of oral samples. Cellular heterogeneity is important to take into account in a wide range of downstream applications 2 , 9 , 14 , 16 , 19 – 21 . Therefore, we recommend that buccal swabs are preferred over saliva samples for studies of cellular function and that cell counts are performed where practical, especially where there are no established methods for post-hoc adjustment for cellular heterogeneity.…”

Confined blood chimerism in a monochorionic dizygotic sex discordant twin pregnancy conceived after induced ovulation

“…For all cases, except three (Aoki et al, ; Walker et al, ; Assaf et al, ), dizygosity was suspected because of a sex discordant phenotype. Furthermore, for all cases except one (Fumoto et al, ) chimerism was confined to the blood. Only two studies in addition to ours have clearly demonstrated blood chimerism by the presence of four parental alleles (Walker et al, ).…”

“…Depending on the cleavage stage, pregnancy is classified as bichorial biamniotic, monochorial biamniotic, or monochorial monoamniotic. Several cases of monochorial dizygotic twin pregnancies have been reported (Viëtor et al, ; Ginsberg et al, ; Quintero et al, ; Souter et al, ; Williams et al, ; Aoki et al, ; Walker et al, ; Ekelund et al, ; Hackmon et al, ; Assaf et al, ; Chen et al, ; Kanda et al, ; Fumoto et al, ). Thus, a monochorionic pregnancy is not always monozygotic.…”

Haematological chimerism masquerading as disorder of sex development

“…The probability of these two events occurring together in the same pregnancy would be exceptionally low. Fumoto et al previously reported a case of chimerism of buccal membrane cells in a monochorionic dizygotic twin . The authors excluded contamination of buccal samples by blood cells through microscopic examination and immunofluorescence.…”