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Fragile X syndrome with extra microchromosome
I López-Pajares1, A Delicado, I Pascual-Castroviejo
1Sección de Genética Médica, Hospital La Paz, Madrid, Spain.
Clinical Genetics
|April 1, 1994
Summary
Molecular analysis is crucial for diagnosing fragile X syndrome, especially in cases with unusual cytogenetic results. This study highlights its importance when standard tests are negative but X-linked intellectual disability is suspected.
Area of Science:
- Genetics
- Molecular Biology
- Clinical Diagnostics
Background:
- Martin-Bell syndrome (Fragile X syndrome) is a leading genetic cause of intellectual disability.
- Cytogenetic studies are standard for diagnosis but can yield false negatives.
Purpose of the Study:
- To investigate a case of suspected fragile X syndrome with atypical cytogenetic findings.
- To evaluate the utility of molecular DNA analysis in such complex cases.
Main Methods:
- Cytogenetic analysis including fragile X (fra X) testing.
- Molecular DNA analysis using the St B 12.3 probe.
- Family-wide genetic studies.
Main Results:
- The proband presented with a microchromosome and was cytogenetically fra X negative.
- Two other affected males in the family were confirmed fra X positive (24% and 26%).
- All affected males, including the proband, showed a similar full mutation via molecular analysis.
Conclusions:
- Molecular analysis is essential for accurate fragile X syndrome diagnosis, particularly when cytogenetic results are inconclusive.
- This case underscores the limitations of cytogenetics and the power of molecular techniques in identifying X-linked intellectual disability.