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Three different origins for apparent triploid/diploid mosaics.
Art Daniel1, Zhanhe Wu, Artur Darmanian
1Departments of Cytogenetics, Western Sydney Genetics Program, The Children's Hospital at Westmead, P/O Box 3515, Parramatta, NSW 2124, Australia. artd@chw.edu.au
Prenatal Diagnosis
|July 18, 2003
Summary
This study investigated triploid/diploid mosaicism, identifying three origins: chimerism, delayed digyny, and delayed dispermy. Mosaicism, not chimerism, was confirmed in most cases, with implications for understanding genetic abnormalities.
Area of Science:
- Genetics
- Reproductive Biology
- Developmental Biology
Background:
- Triploid/diploid mosaicism, a condition involving cells with both triploid and diploid chromosome numbers, presents complex origins and developmental outcomes.
- Understanding the mechanisms behind mosaicism is crucial for accurate prenatal diagnosis and genetic counseling.
Observation:
- Four cases of apparent triploid/diploid mosaicism were analyzed, including prenatal diagnoses and a dysmorphic individual.
- Karyotyping across multiple tissues and microsatellite analysis were employed to differentiate between mosaicism and chimerism.
- Three distinct origins were identified: chimerism, delayed digyny (second polar body incorporation), and delayed dispermy (second sperm incorporation).
Findings:
- Three cases exhibited true mosaicism, confirmed by DNA analysis showing consistent allele patterns across cell lines.
- One case was identified as chimerism, with distinct karyotypes in different cell lines (47,XY,+16 and 69,XXY), suggesting a diploid ovum origin.
- Delayed digyny and dispermy were implicated as mechanisms for mosaicism, involving the incorporation of a second polar body or sperm pronucleus, respectively.
- Confined placental mosaicism was observed in one case, where the triploid cell line was restricted to placental tissues, with the fetus developing normally.
Implications:
- Differentiating between mosaicism and chimerism is critical for accurate genetic diagnosis and prognosis.
- The identified mechanisms of delayed gamete incorporation offer insights into the etiology of polyploidy.
- The potential for normal fetal development despite mosaicism, particularly in cases of confined placental mosaicism, highlights the complexity of chromosomal abnormalities.