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.
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.
Kotzot
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Institut für Medizinische Genetik, Universität Zürich, Switzerland.
Schinzel
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A
D000365:Age Determination by Skeleton; D002648:Child; D002869:Chromosome Aberrations / Q000235:genetics*; D025063:Chromosome Disorders; D004314:Down Syndrome / Q000235:genetics*; D005260:Female; D005819:Genetic Markers / Q000235:genetics; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007223:Infant; D007231:Infant, Newborn; D007621:Karyotyping; D008297:Male; D008540:Meiosis / Q000235:genetics*; D009030:Mosaicism / Q000235:genetics*; D010375:Pedigree; D011247:Pregnancy
D005819:Genetic Markers