What causes mosaic Down syndrome?

Updated: Apr 30, 2018
  • Author: Gratias Tom Mundakel, MBBS, DCH; Chief Editor: Maria Descartes, MD  more...
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Most patients with mosaic Down syndrome were once trisomy 21 zygotes. The phenotype varies and possibly reflects the variable proportion of trisomy 21 cells in the embryo during early development. In rare instances, low-level mosaicism in the germinal tissue of a parent is postulated to be the cause of having more than one trisomic child in a family. Many geneticists believe that all full trisomy 21 patients are mosaic at some level.

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