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Chromosome mosaicism in 6,000 amniocenteses
M G Wilson1, M S Lin, A Fujimoto
1Department of Pediatrics, University of Southern California School of Medicine, Los Angeles County.
American Journal of Medical Genetics
|April 1, 1989
Summary
Mosaicism in amniocentesis, detected in 0.20% of cases, often involves sex chromosomes. While most cases show normal phenotypes, some autosomal abnormalities like del(18q) are linked to fetal issues.
Area of Science:
- Genetics
- Prenatal Diagnosis
- Cytogenetics
Background:
- Mosaicism, the presence of two or more cell lines with different genotypes, can occur during fetal development.
- Amniocentesis is a common prenatal diagnostic procedure for detecting chromosomal abnormalities.
- Understanding mosaicism is crucial for accurate genetic counseling and risk assessment.
Purpose of the Study:
- To investigate the incidence and implications of different types of mosaicism detected through amniocentesis.
- To correlate cytogenetic findings with phenotypic outcomes in cases of fetal mosaicism.
- To assess the reliability of amniotic fluid cell cultures in identifying true fetal mosaicism versus in vitro artifacts or maternal cell contamination.
Main Methods:
- Analysis of 6,000 amniocentesis cases to identify and classify mosaicism.
- Examination of fetal or infant tissues at delivery or elective abortion for confirmation of mosaicism.
- Correlation of cytogenetic findings (sex chromosome abnormalities, autosomal abnormalities) with clinical phenotypes.
Main Results:
- Multiple cell-multiple flask mosaicism was identified in 0.20% of cases, frequently involving sex chromosomes (e.g., 45,X/46,XY).
- Multiple cell-single flask mosaicism was found in 0.92% of cases.
- Most sex chromosome mosaicism cases had normal phenotypes, with one exception (45,X/46,XX with aortic coarctation).
- Autosomal abnormalities, such as del(18q), were associated with fetal anomalies, while trisomy 17, marker chromosomes, and monosomy 21 showed normal phenotypes.
- Maternal cell contamination was observed in 0.49% of cases, highlighting the importance of examining multiple culture vessels.
Conclusions:
- While sex chromosome mosaicism is often benign, certain autosomal abnormalities detected via amniocentesis can be associated with significant fetal anomalies.
- The distinction between true fetal mosaicism and in vitro artifacts or maternal contamination is critical for accurate diagnosis.
- Continued monitoring of individuals with confirmed mosaicism, even with normal initial phenotypes, is important.