FMR1 and fragile X syndrome: Interestingly, despite the expression of FMR1 in FXS 3, the methylation profile of this cell line closely approximates the CpG methylation signature of the FXS- cohort, with an average percent methylation of 70.90% ± 2.41% (HDFs), 81.5% ± 2.5% (hiDFPs), and 79.0% ± 3.11% in hiDFP-derived neurons.