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Mosaicism in fragile X affected males
S L Nolin1, A Glicksman, G E Houck
1New York State Institute for Basic Research in Developmental Disabilities, Staten Island 10314.
American Journal of Medical Genetics
|July 15, 1994
Summary
Mosaicism, involving premutation and full mutation Fragile X syndrome (FXS) alleles, is common in affected males. This study found 41% of males with FXS were mosaic, a higher rate than previously reported, suggesting mosaicism is a frequent event.
Area of Science:
- Genetics
- Molecular Biology
- Neurodevelopmental Disorders
Background:
- Fragile X syndrome (FXS) in males is characterized by CGG repeat expansion and FMR-1 gene hypermethylation.
- Mosaicism, presenting with both premutation and full mutation alleles, occurs in FXS.
- Identifying mosaic males is crucial for understanding FXS genetics and presentation.
Purpose of the Study:
- To determine the frequency of mosaicism in males affected with Fragile X syndrome.
- To investigate potential familial patterns of mosaicism in FXS.
- To highlight the diagnostic significance of mosaicism in FXS.
Main Methods:
- Southern blotting analysis using EcoR I, Eag I, and StB12.3 probe.
- Analysis of 148 affected males, including 36 pairs of brothers and 76 unrelated individuals.
- Detection of methylated full mutation and unmethylated premutation fragments.
Main Results:
- 41% (61/148) of affected males with FXS were identified as mosaic.
- No significant difference in mosaicism rates was observed between brothers and unrelated males.
- The observed frequency of mosaicism (41%) is substantially higher than previously reported.
Conclusions:
- Mosaicism is a frequent occurrence in males with Fragile X syndrome, potentially more common than previously recognized.
- The study did not find evidence supporting a familial basis for mosaicism in FXS.
- Technical improvements in Southern blotting likely contributed to the higher detection rate of mosaic individuals.