Young Brisbane twins, a boy and a girl, have been identified as the only other set of semi-identical or sesquizygotic twins in the world – and the first to be identified by doctors during pregnancy.
"It is likely that the mother's eggs are simultaneously fertilized by two of the father's sperm cells before they split," said Professor Fish, who led the maternal and twins foster medicine team, based on Royal Brisbane and Women & # 39 ; s Hospital in 2014. Professor Fisk, a former president of the International Fetal Medicine and Surgery Society, worked with Dr. Gabbett.
"The mother's ultrasound in six weeks showed a single placenta and placement of fetuses that showed she expected identical twins. A 1
Dr. Gabbett said that if an egg is fertilized by two sperm, it results in three sets of chromosomes, one from the mother and two from the father.
"Three sets of chromosomes are typically incompatible with life, and embryos usually do not survive," he said.
"In the case of Brisbane's sesquizygotic twins, the fertilized egg appears to have evenly divided three sets of chromosomes into groups of cells, which are then divided into two, creating the twins.
" Some of the cells contain the chromosomes of the first seed, while the remaining cells contain chromosomes from the second semen, resulting in the twins only sharing a proportion rather than 100 percent of the same fathers DNA. "
Sesquizygotic twins were first reported in the United States in 2007. These twins came to the doctors' attention in childhood when identified with ambiguous genitals. Study of mixed chromosomes, doctors found that the boy and the girl were identical on their mother's side, but shared about half of their fathers DNA.
Professor Fisk said an analysis of worldwide twin databases pointed out how rare sesquizygotic twins are.
"We first questioned whether there might be other cases that was incorrectly classified or not reported, so genetic data from 968 examined fraternal twins and their parents, "he said.
" However, we did not find other sesquizygotic twins in this data, nor any cases of semi-identical twins in large global twin studies.
"We know this is an unusual case of semi-identical twins. While doctors can recall seemingly identical twins, it rarely means that there is no case for routine genetic testing."
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