Mosaicism for full mutation and normal-sized allele of the FMR1 gene: a new case.
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 normal-sized 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.
Orrico
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Department of Molecular Biology, Medical Genetics, Università degli Studi di Siena, Italy. geneticamed@unisi.it
Galli
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Dotti
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Plewnia
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Censini
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Federico
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D000328:Adult; D000483:Alleles; D015139:Blotting, Southern; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D005091:Exons / Q000235:genetics; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics*; D005820:Genetic Testing; D006801:Humans; D008297:Male; D009030:Mosaicism; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D016601:RNA-Binding Proteins; D017384:Sequence Deletion; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D018911:Trinucleotide Repeats / Q000235:genetics
D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human