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. 2019 Feb 28;380(9):842-849.
doi: 10.1056/NEJMoa1701313.

Molecular Support for Heterogonesis Resulting in Sesquizygotic Twinning

Michael T Gabbett  1 , Johanna Laporte  1 , Renuka Sekar  1 , Adayapalam Nandini  1 , Pauline McGrath  1 , Yadav Sapkota  1 , Peiyong Jiang  1 , Haiqiang Zhang  1 , Trent Burgess  1 , Grant W Montgomery  1 , Rossa Chiu  1 , Nicholas M Fisk  1
Affiliations

Molecular Support for Heterogonesis Resulting in Sesquizygotic Twinning

Michael T Gabbett et al. N Engl J Med. .

Abstract

Sesquizygotic multiple pregnancy is an exceptional intermediate between monozygotic and dizygotic twinning. We report a monochorionic twin pregnancy with fetal sex discordance. Genotyping of amniotic fluid from each sac showed that the twins were maternally identical but chimerically shared 78% of their paternal genome, which makes them genetically in between monozygotic and dizygotic; they are sesquizygotic. We observed no evidence of sesquizygosis in 968 dizygotic twin pairs whom we screened by means of pangenome single-nucleotide polymorphism genotyping. Data from published repositories also show that sesquizygosis is a rare event. Detailed genotyping implicates chimerism arising at the juncture of zygotic division, termed heterogonesis, as the likely initial step in the causation of sesquizygosis.

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