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Trisomy/tetrasomy 21 mosaicism in CVS: interpretation of cytogenetic discrepancies between placental and fetal chromosome complements
  1. Anna Soler,
  2. Ester Margarit,
  3. Ana Carrió,
  4. Dolors Costa,
  5. Rosa Queralt,
  6. Francisca Ballesta
  1. Servei de Genètica, Hospital Clínic i Provincial de Barcelona, Villarroel 170, 08035 Barcelona, Spain
  1. Dr Soler.

Abstract

Trisomy/tetrasomy 21 mosaicism was found in chorionic villi (semidirect preparation) obtained from a 40 year old pregnant woman. Since both cell lines were abnormal, the couple elected for pregnancy termination. Placenta and fetal tissue samples were obtained for cytogenetic study. Long term cultured villi showed a non-mosaic trisomy 21 karyotype, while other tissues showed either a normal karyotype or normal/trisomy21 mosaicism. These discrepancies could be explained by a modified “bottle neck” embryogenic model with a trisomic zygote and a non-disjunction event taking place in one of the first divisions. Our case emphasises the need for confirmatory studies in other tissues when mosaicism is encountered in chorionic villi, even if all cell lines are abnormal.

  • confined placental mosaicism
  • trisomy/tetrasomy 21
  • embryogenic models

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