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Such is the case with the report by Fumoto and colleagues at the Kyorin University School of
Medicine’s HLA laboratory in Kyoto, Japan (doi: 10.1542/peds.2013-1938). Not until recently has the existence of monochorionic dizygotic twins (MCDZT) been known.
Prior to work by Souter et al. in 2003, monochorionic twins were believed to all be monozygous. Subsequent to Souter’s publication, MCDZT were recognized to be not extremely rare particularly in pregnancies by in vitro fertilization. Once such twins were recognized blood chimerism between such twins was noted to occur fairly often. Blood derived from one zygote was found in the blood stream of the twin derived from the other zygote and vice versa.
This finding, it is assumed, occurs when placental vessels cross during in-utero development mixing one twins blood elements with the others. Until Fumoto’s report, only blood elements were known to be chimeric in MCDZT and only on occasion. Fumoto upsets that notion by finding chimeric buccal cells in each of a twin set. The authors speculate on the mechanism of this finding and possible implications of its occurrence in the report.
It appears that the more deeply we look into biology, the more we find exceptions that no doubt are new harbingers of deeper understanding of nature’s overall plan.