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Mosaicism for full mutation and normal-sized allele of the FMR1 gene: A new case

✍ Scribed by Orrico, Alfredo; Galli, Lucia; Dotti, Maria Teresa; Plewnia, Katrin; Censini, Stefano; Federico, Antonio


Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
15 KB
Volume
78
Category
Article
ISSN
0148-7299
DOI
10.1002/(sici)1096-8628(19980724)78:4<341::aid-ajmg7>3.0.co;2-o

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✦ Synopsis


The main mutation in fragile X patients is the expansion of the CGG repeat in the first exon of the FMR1 gene, associated with hypermethylation of the proximal CpG island. An increasing number of atypical cases have been reported showing the coexistence of full mutation and premutated or normalsized alleles. These genotypes are more difficult to detect, and if a PCR strategy alone is adopted, they can be incorrectly identified. We report on a fragile X man with severe phenotype and mosaicism for full mutation and a (CGG) 7 normal allele, the shortest fragment reported as yet in mosaics. This case of mosaicism, as other similar cases previously reported, suggests that the normal-length allele can derive from a deletion during the same early stage of development in which the full mutation expansion also arose. Am.


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