FMR1 and fragile X syndrome: Since the distinction between a premutation and a full mutation is related to the methylation status rather than to the exact size of the repeat, in the present study we evaluated the usefulness of the Methylation-Specific Multiplex-Ligation-dependent Probe Amplification (MS-MLPA) assay to assess the methylation status of the promoter of the FMR1 gene for the molecular diagnosis of FXS.