Trisomy 20 mosaicism confirmed in a phenotypically normal liveborn.

Area of Science:

• Genetics
• Prenatal Diagnosis
• Developmental Biology

Background:

• Mosaicism, characterized by the presence of two or more cell lines with different genetic constitutions, can occur during early development.
• Trisomy 20 mosaicism, a rare condition involving an extra copy of chromosome 20 in some cells, presents diagnostic challenges due to variable clinical manifestations.
• Accurate prenatal diagnosis is crucial for genetic counseling and management of pregnancies involving chromosomal abnormalities.

Observation:

• Prenatal diagnosis identified trisomy 20 mosaicism in cultured amniotic fluid cells (23/252 cells).
• Postnatal confirmation revealed mosaicism in cultured foreskin fibroblasts (7/49 cells) and placental cells (20/20 cells).
• Peripheral lymphocytes of the neonate were cytogenetically normal (46,XY).

Findings:

• This case represents the first documented confirmation of trisomy 20 mosaicism in a phenotypically normal full-term neonate.
• The study highlights discrepancies in chromosomal findings between different fetal tissues (amniotic fluid, placenta, fibroblasts) and postnatal tissues (lymphocytes).
• The genetic findings suggest that trisomy 20 mosaicism can be present without discernible phenotypic abnormalities at birth.

Implications:

• This finding expands the understanding of the phenotypic spectrum associated with trisomy 20 mosaicism.
• It underscores the importance of comprehensive cytogenetic analysis using multiple tissue types for accurate diagnosis and risk assessment.
• Further research is needed to elucidate the mechanisms underlying the resolution of mosaicism and its correlation with clinical outcomes.