Friday, April 22, 2011

The twin within: (5) A mosaic twin

Identical twins, as I have said ad nauseam, are not identical, and for this reason they are best called "monozygotic twins"  -  term that refers only to the fact they they arise out of one zygote and not to how similar they are to look at or in other, deeper ways.  Both sets of DNA are almost identical, but some of the chromosomes in some cells, but not all, have become abnormal. If you have some normal cells and some abnormal cells in your body then you are a mosaic.

A mosaic twin is someone with  a variation in DNA that arises out of monozygotic twinning when the chromosomes in the body of one twin are altered after the zygote has split.  It can happen that one twin is a mosaic, that is the chromosome set becomes abnormal ( such as having 47 chromosomes  instead of 46) while the other twin remains normal.  The twins may share blood with altered DNA because of the shared placental blood supply, and if the mosaic twin dies, then the survivor is left with no other signs of abnormality except the mosaic blood they both once shared.

As one researcher put it:
Postzygotic chromosomal rearrangement may have occurred early in one embryo after the twinning event,.......

How would that feel psychologically to the sole survivor in this case?  To feel as if one is some way "abnormal" or "not properly developed as a human being"?

Is this like having another, less-developed and imperfect version of yourself somewhere inside you?

In  Human chromosomes By Orlando J. Miller, Eeva Therman  they wrote: Given the frequencies of non disjunction and chromosome loss throughout life, we are all mosaics to some degree.

At the risk of repeating myself, we have a lot more  to learn about mosaicism and whether it is a sign of being a womb twin survivor.

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