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Monozygotic twins discordant for trisomy 21
American Journal of Medical Genetics
|February 1, 1982
Summary
This study examines a rare case of monozygotic twins discordant for Down syndrome. Mosaicism in both twins, identified through lymphocyte and fibroblast analysis, likely resulted from placental vascular connections.
Area of Science:
- Genetics
- Developmental Biology
- Perinatology
Background:
- Monochorionic twins share a placenta, increasing risks of vascular anastomoses.
- Phenotypic discordance in identical twins suggests post-zygotic genetic events.
- Down syndrome (Trisomy 21) is typically associated with complete trisomy.
Observation:
- A pair of monochorionic twins presented with phenotypical discordance for Down syndrome.
- Lymphocyte chromosome analysis revealed mosaicism in both twins.
- Fibroblast analysis confirmed one twin as 46,XY and the other as 47,XY,+21.
Findings:
- The observed blood mosaicism is attributed to placental vascular anastomoses between the twins.
- The twins were confirmed as monozygotic based on placentation, blood groups, HLA haplotypes, and serum proteins.
- This case represents a rare occurrence of Down syndrome discordance in monozygotic twins.
Implications:
- Placental anastomoses can lead to genetic mosaicism and phenotypic discordance in monochorionic twins.
- Understanding these events is crucial for accurate genetic counseling and diagnosis in twin pregnancies.
- Further research into the mechanisms of zygotic splitting and placental development is warranted.