Médecine moléculaire et génétique

Tissue-Specific Size and Methylation Analysis in Two Fragile X Families: Contribution to the Clinical Phenotype

Abstract

Edith RQM, Silvia J, Inmaculada R, Alicia G, Raquel M, Pablo M and Elizabeth P

Methylation at critical CpG sites on the expanded FMR1 gene is crucial for pathological manifestation of fragile X syndrome and fragile X-related disorders. Methylation status from blood, oral mucosa and root hair was analyzed with the FMR1 mPCR kit (Asuragen). Differential allele expression was studied by TP-PCR. Psychological and neurological explorations were performed in the probands. Patient II-1 of family 1 showed an extremely skewed X-chromosome inactivation of the normal allele in blood, oral mucosa cells and root hair. Analysis of differential expression of both alleles in blood showed the preferential expression of the expanded allele. Similarly, patient II-3 of family 2 showed an extremely skewed X-chromosome inactivation of the normal allele in blood, oral mucosa and root hair. Both females presented clinical features compatible with their skewed methylation toward the normal allele. Methylation analysis at critical CpG sites in the first FMR1 exon may predict clinical manifestations in carriers of premutation or full mutation. Analysis of differential expression of both alleles in women using TP-PCR could contribute to clarify the real impact of skewed methylation on the phenotype.