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Two Prader-Willi/Angelman syndrome loci present in an isodicentric marker chromosome
S Luke1, R S Verma, R Giridharan
1Division of Genetics, Long Island College Hospital, Brooklyn, New York.
Abstract:
We found an abnormal 47,XX,+mar karyotype in a patient with developmental delay, hypotonia, microcephaly, failure to thrive, and cognitive delay. When metaphases were hybridized with Prader-Willi and Angelman loci-specific probes by the FISH technique, two sites were noted at opposite positions on the marker chromosome. The alphoid satellite DNA probe documented the isodicentric nature while retention of the p arms on both sides of the marker chromosome was demonstrated by beta satellite probe. The patient does not exhibit manifestations of either syndrome despite the presence of these loci in tetrasomic dose. The present investigation suggests that other marker chromosomes be reevaluated, as their clinical manifestations are quite variable.
Insights
A rare marker chromosome (mar) was found in a patient with developmental delays. Despite containing Prader-Willi and Angelman gene regions, the patient showed no symptoms of these genetic disorders.
Area of Science:
- Genetics
- Cytogenetics
- Developmental Biology
Background:
- Karyotyping is crucial for diagnosing genetic disorders.
- Marker chromosomes can lead to variable clinical presentations.
- Prader-Willi and Angelman syndromes are complex genetic disorders.
Observation:
- A patient presented with developmental delay, hypotonia, microcephaly, failure to thrive, and cognitive delay.
- Karyotype analysis revealed an abnormal 47,XX,+mar.
- Fluorescence in situ hybridization (FISH) identified Prader-Willi and Angelman loci on the marker chromosome.
Findings:
- The marker chromosome was isodicentric, with retained p arms on both sides.
- The presence of Prader-Willi and Angelman loci in tetrasomic dose did not cause the expected clinical manifestations.
- This case highlights the complexity of genotype-phenotype correlations in marker chromosome disorders.
Implications:
- Reevaluation of marker chromosomes is necessary due to variable clinical outcomes.
- Understanding the function of marker chromosomes requires further investigation.
- This study contributes to the knowledge of rare chromosomal abnormalities and their impact on development.