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A common fragile site at Xq27: theoretical and practical implications
1Institute for Molecular Genetics, Baylor College of Medicine, Houston, TX 77030.
American Journal of Human Genetics
|May 1, 1988
Summary
A common fragile site (FRAXD) exists at Xq27, inducible in normal individuals and ancestral to humans and chimpanzees. This finding may explain low-level fragile-X expression and its link to Martin-Bell syndrome.
Area of Science:
- Genetics
- Cytogenetics
- Human Genetics
Background:
- The fragile site at Xq27 (FRAXA) is linked to X-linked mental retardation (Martin-Bell syndrome) and typically considered rare.
- Previous research showed low-level fragile-X expression in normal X chromosomes under thymidylate stress.
Purpose of the Study:
- To investigate the presence and inducibility of fragile sites at Xq27 in normal individuals.
- To determine if a common fragile site exists at Xq27, potentially related to FRAXA.
Main Methods:
- Induction of fragile-X expression in lymphocytes and lymphoblasts using high-dose aphidicolin (1.5 microM).
- Analysis of fragile-X expression levels in control males and male chimpanzees.
Main Results:
- Significantly higher levels of fragile-X expression (6%-28%) were induced in control males.
- Similar high expression levels (10%-12%) were observed in normal male chimpanzees.
- These results indicate a common fragile site at Xq27 (FRAXD), ancestral to humans and chimpanzees.
Conclusions:
- Xq27 harbors a common fragile site (FRAXD) that is evolutionarily conserved.
- FRAXD may be the substrate for recombination events leading to the rare FRAXA site associated with Martin-Bell syndrome.
- The presence of FRAXD can explain occasional low-level fragile-X expression in normal individuals, necessitating caution in diagnostic interpretations.