FMR1 and fragile X syndrome: While methylation percentage provided by this approach may not represent methylation of the larger FMR1 promoter as it provides average methylation for only two HpaII methylation sensitive restriction sites (one within the FMR1 CpG island and the other within FMR1 exon 1) (Figure 2A), methylation of these sites has been shown to be elevated in FXS males [16].