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Characterization of i(18p) in prenatal diagnosis by fluorescence in situ hybridization
1Department of Laboratory Medicine, University of California, San Francisco.
Abstract:
A case is presented in which chorionic villus direct preparation and cultured chorionic villus cells revealed a 47,XX+mar karyotype. The marker was a small metacentric chromosome and appeared to be i(18p)--isochromosome 18p. Follow-up studies in both amniotic fluid and fetal fibroblasts confirmed the karyotype. In order to characterize the marker, a panel of biotinylated DNA probes was used, including a whole chromosome 18 probe, chromosome 18-specific alpha satellite DNA, Yac clones, and a pan-telomeric probe. These studies show that the marker is a monocentric i(18p) in which about 80 per cent of chromosome 18 alpha satellite DNA has been lost.
Insights
Genetic testing revealed an isochromosome 18p (i(18p)) in fetal cells. This marker chromosome, identified through chorionic villus sampling and amniotic fluid analysis, is monocentric with significant alpha satellite DNA loss.
Area of Science:
- Cytogenetics
- Molecular Genetics
- Prenatal Diagnosis
Background:
- Karyotyping is crucial for identifying chromosomal abnormalities during prenatal diagnosis.
- Isochromosome 18p (i(18p)) is a rare structural variation involving duplication of the short arm of chromosome 18.
- Accurate characterization of marker chromosomes is essential for genetic counseling.
Observation:
- A case of fetal karyotype 47,XX+mar was identified using chorionic villus sampling.
- The marker chromosome was characterized as a small metacentric chromosome, suspected to be i(18p).
- Follow-up studies using amniotic fluid and fetal fibroblasts confirmed the presence of the marker chromosome.
Findings:
- Molecular probes, including whole chromosome 18, alpha satellite DNA, Yac clones, and telomeric probes, were used to characterize the marker.
- The marker was confirmed to be a monocentric i(18p).
- Approximately 80% of chromosome 18 alpha satellite DNA was found to be lost in the marker chromosome.
Implications:
- This detailed characterization of i(18p) contributes to the understanding of structural chromosomal abnormalities.
- Accurate identification of such markers is vital for assessing potential developmental outcomes and providing genetic counseling.
- Further research may elucidate the clinical significance and long-term effects of this specific i(18p) variant.