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Prenatally detected trisomy 20 mosaicism
W P Robinson1, B McGillivray, M E S Lewis
1Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada. wprobins@interchange.ubc.ca
Prenatal Diagnosis
|March 26, 2005
Summary
Trisomy 20 mosaicism detected during pregnancy typically results in a normal outcome. However, high levels of trisomic cells in amniotic fluid are linked to adverse outcomes like developmental delay or stillbirth.
Area of Science:
- Prenatal genetics
- Reproductive medicine
- Human genetics
Background:
- Mosaic trisomy 20 is frequently identified via amniocentesis, usually with favorable outcomes.
- Abnormal fetal development, including growth restriction and congenital anomalies, has been anecdotally linked to trisomy 20.
- The influence of trisomy origin and uniparental disomy on trisomy 20 outcomes remains unclear.
Observation:
- This study analyzed six cases of trisomy 20 mosaicism, diagnosed through chorionic villous sampling and amniocentesis.
- Molecular studies were performed to investigate the origin of trisomy and rule out uniparental disomy.
Findings:
- A meiotic origin was confirmed in only one case; uniparental disomy was excluded in all tested families.
- Low levels of trisomy 20 in amniotic fluid (<40%) correlated with normal outcomes in 96% of cases.
- High trisomy 20 levels (≥40%) were associated with abnormal outcomes, including developmental delay and stillbirth.
Implications:
- The level of trisomy 20 mosaicism in amniotic fluid is a critical predictor of fetal outcome.
- Prenatal diagnosis of trisomy 20 requires careful assessment of cell levels to counsel families effectively.
- Further research into the genetic mechanisms underlying trisomy 20 mosaicism is warranted.
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