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Cryptic familial t(11;18)(q25;q23) incidentally detected by interphase FISH
L N Schultz1, P Schmidt, A Tabor
1Cytogenetic Laboratory, Department of Clinical Genetics, Juliane Marie Center, Rigshospitalet, Copenhagen, Denmark.
Clinical Genetics
|April 12, 2001
Summary
A cryptic translocation between chromosomes 11 and 18 was discovered in a family, impacting multiple generations. This balanced translocation, often missed by standard karyotyping, can lead to developmental issues in offspring.
Area of Science:
- Genetics
- Prenatal Diagnosis
- Human Molecular Cytogenetics
Background:
- Standard G-banded karyotyping can miss cryptic chromosomal rearrangements.
- Prenatal diagnosis relies on accurate detection of numerical and structural chromosomal abnormalities.
Purpose of the Study:
- To investigate an incidental finding of a single chromosome 18 signal during prenatal diagnosis.
- To identify the underlying cause of mental retardation in a family with a suspected chromosomal abnormality.
Main Methods:
- Prospective prenatal study using locus-specific probes for chromosome enumeration.
- Chorionic villus sampling (CVS) for fetal genetic analysis.
- G-banded karyotyping and subtelomeric probe analysis for translocation detection.
Main Results:
- A cryptic balanced reciprocal translocation t(11;18) was identified in the father, missed by G-banding.
- An unbalanced translocation der(18)t(11;18) was found in the fetus, leading to a monosomy 18 phenotype.
- The translocation was present in balanced and unbalanced forms across four generations, correlating with intellectual disability.
Conclusions:
- Cryptic translocations require advanced molecular cytogenetic techniques for accurate diagnosis.
- Early genetic counseling and testing are crucial for families with recurrent chromosomal abnormalities.
- Molecular cytogenetics is essential for diagnosing dysmorphic and intellectually disabled children with normal karyotypes.