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Twins with 'Chimerism'

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Twins with 'Chimerism'

Post by Upsy Daisy on 26.11.11 15:00

Interesting information about a certain type of twins common to those born from IVF. Had Madeleine been a Chimera twin, her blood type would be easily identifiable if her medical records were produced. Would discovering this information enable forensics to identify her DNA without a shadow of a doubt?


Chimerism - A chimera is a person composed of TWO different types of cells. This can occur from a twin absorbing another in the womb, and will only be detectable if it is fraternal twins that merge. These individuals will sometimes have two different blood types (their own and that of their twin). Chimerism is quite rare, there have only been around 45 detected (but again, if identical twins were to merge, no one would be able to discover it). A true chimera is considered a person whose non-identical twin was merged with them, and they carry some genetic evidence of this twin, in their blood or other parts of their body. Chimerism can also occur between living twins.

Chimerism is said to occur more frequently among IVF babies.

Cases

A woman in Boston, reported in New Scientist magazine - it was discovered when she needed a kidney transplant and her children's haplotypes (a block of genes) were different from hers (they should have been the same). The mother had 2 sets of haplotypes herself, one set of hers, the other a twin sister's. She had twice the chance to match haplotypes for her transplant, as she had 2 sets.

Patricia McDonnell of England discovered when she was pregnant and going through blood tests that she carried 2 blood types - O and A. About 93% of her blood was type O, and 7% type A. The scientists concluded after more than 3 years of tests, that the type A blood was her own, as the type O blood belonged to her twin brother. I believe this case was first reported in 1953.

In British Columbia, one twin had cystic fibrosis (according to sweat tests), but her blood did not. Her assumed identical twin did not have it, and when blood tested, neither twin had CF and they were discovered to be genetically fraternal. In the womb, their placentas had fused and they had shared circulation, so much so that the healthy twin took over for the sick twin. So the sick twin had cystic fibrosis in her body, but not her blood.



Something to ponder over.

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Upsy Daisy

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