Paternal meiotic origin of der(21;21)(q10;q10) mosaicism [46,XX/46, XX,der(21;21)(q10;q10),+21] in a girl with mild Down syndrome

Eur J Hum Genet. 2000 Sep;8(9):709-12. doi: 10.1038/sj.ejhg.5200520.


Mosaicism for a derivative 21, der(21;21)(q10;q10), is a rare chromosomal abnormality. Since a normal cell line is present, mitotic origin is considered. Chromosome examination of a female with developmental delay and dysmorphic features compatible with mosaic trisomy 21 revealed a normal cell line and a second cell line with a der(21;21)(q10;q10) [46,XX/46,XX,der(21;21)(q10;q10),+21]. Molecular investigation with a panel of highly polymorphic microsatellites mapping to chromosome 21 demonstrated three different alleles, two of paternal and one of maternal origin. Therefore, either formation of the der(21;21)(q10;q10) during paternal meiosis with subsequent loss of the der(21;21)(q10;q10) and mitotic reduplication of the maternal homologue in the normal cell line, or more likely a zygote with paternally derived trisomy 21 and subsequent mitotic formation of the der(21;21)(q10;q10) have to be considered. This case again shows that mammalian chromosome aberrations may have a more complex mechanism of formation than was previously thought.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Determination by Skeleton
  • Child
  • Chromosome Aberrations / genetics*
  • Chromosome Disorders
  • Down Syndrome / genetics*
  • Female
  • Genetic Markers / genetics
  • Humans
  • In Situ Hybridization, Fluorescence
  • Infant
  • Infant, Newborn
  • Karyotyping
  • Male
  • Meiosis / genetics*
  • Mosaicism / genetics*
  • Pedigree
  • Pregnancy


  • Genetic Markers