Variable outcomes in mosaic trisomy 16: five case reports and literature analysis

Area of Science:

• Genetics
• Prenatal Diagnosis
• Fetal Medicine

Background:

• Mosaic trisomy 16 is a chromosomal abnormality with variable clinical presentations.
• Understanding its impact on fetal development and pregnancy outcomes is crucial for genetic counseling.

Observation:

• Five new cases of mosaic trisomy 16 were analyzed alongside 125 reported cases.
• Prenatal detection methods and outcomes were examined to identify patterns.

Findings:

• Intrauterine growth restriction (IUGR), premature delivery, and physical anomalies are common, irrespective of trisomy confinement to the placenta.
• Amniotic fluid mosaicism for trisomy 16 may indicate true mosaicism with phenotypic effects.
• Fluorescence in situ hybridization (FISH) shows higher sensitivity than traditional cytogenetics for detecting mosaicism.
• Elevated hCG and MS-AFP levels are frequently observed.
• Uniparental disomy (UPD) exacerbates IUGR and anomalies in confined placental mosaicism (CPM).

Implications:

• While no distinct syndrome exists, IUGR and cardiac defects are frequent in mosaic trisomy 16.
• Approximately 20% of cases result in normal outcomes; others may present with prematurity, IUGR, or minor/repairable birth defects.
• Accurate prenatal detection and understanding of mosaic trisomy 16 are vital for managing pregnancy and counseling families.