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Prenat Diagn. 2007 Jun;27(6):552-4.

Prenatal diagnosis in monozygotic twins with Down syndrome who had different phenotypes.

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CHU Reims, Institut mère-enfant Alix de Champagne, Service de Gynécologie-Obstétrique, 45 rue Cognacq-Jay, F-51092 Reims, France.


We report the case of monozygotic (MZ) male twin fetuses with different Down syndrome (DS) phenotypes. Prenatal fetal sonography showed a bichorial biamniotic pregnancy with increased nuchal translucency in twin A and a cervical cystic hygroma and heart defect in twin B. Cytogenetic analysis performed after double amniocentesis showed free and homogeneous trisomy 21 in both twins. Monozygosity was confirmed by molecular analysis. The pregnancy was terminated at 17 weeks of gestation (WG). Postmortem analysis confirmed the phenotypic discordance. To our knowledge, this is the first reported prenatal diagnosis of MZ male twins with different Down syndrome phenotypes but identical karyotypes. We discuss the mechanisms involved in phenotypic discordance of monozygotic twins and particularly the role of environmental factors.

[Indexed for MEDLINE]

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