• Michael T Gabbett, Johanna Laporte, Renuka Sekar, Adayapalam Nandini, Pauline McGrath, Yadav Sapkota, Peiyong Jiang, Haiqiang Zhang, Trent Burgess, Grant W Montgomery, Rossa Chiu, and Nicholas M Fisk.
• From the School of Biomedical Sciences and the Institute of Health and Biomedical Innovation, Queensland University of Technology (M.T.G.), the School of Medicine (M.T.G., J.L., R.S.), the Institute for Molecular Bioscience (G.W.M.), and the Centre for Clinical Research (N.M.F.), University of Queensland, Genetic Health Queensland (M.T.G., P.M.), the Centre for Advanced Prenatal Care (J.L., R.S., N.M.F.), and the Department of Cytogenetics (A.N.), Royal Brisbane and Women's Hospital, and QIMR Berghofer Medical Research Institute (Y.S., G.W.M.), Brisbane, the School of Medicine, Griffith University, Gold Coast, QLD (M.T.G.), Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC (T.B.), the Department of Pediatrics, University of Melbourne, Royal Children's Hospital, Parkville, VIC (T.B.), and the Faculty of Medicine, University of New South Wales, Sydney (N.M.F.) - all in Australia; and Li Ka Shing Institute of Health Sciences, Department of Chemical Pathology, Chinese University of Hong Kong, Hong Kong (P.J., H.Z., R.C.).
• N. Engl. J. Med. 2019 Feb 28; 380 (9): 842-849.

AbstractSesquizygotic 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.Copyright © 2019 Massachusetts Medical Society.

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