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Updated: Oct 20, 2026

Microsatellite DNA Genotyping and Flow Cytometry Ploidy Analyses of Formalin-fixed Paraffin-embedded Hydatidiform Molar Tissues
Published on: October 20, 2019
[Low-frequency trisomy 21 mosaicism diagnosed following conflicting prenatal testing]
Gerda Ferjá Heldarskard1, Nina Gros Pedersen2, Laura Kirstine Sønderberg Roos3
1Børne- og Ungeafdelingen, Nordsjællands Hospital.
Abstract:
Down syndrome is caused by trisomy 21. Far less common is trisomy 21 mosaicism, in which only a proportion of cells carry the chromosomal abnormality. In this case report, first-trimester combined screening and non-invasive prenatal testing (NIPT) showed an increased risk of trisomy 21. However, chromosomal microarray performed after amniocentesis was normal and confined placental mosaicism was deemed most likely. After birth, the child showed slight stigmata for Down syndrome, and a blood sample confirmed the presence of low-frequency mosaicism at 6 months of age.
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