Interestingly, PCR validation highlighted important inter-individual variations in 5hmC levels across FXS patient samples in most interrogated regions, representing potential inter-individual differences in FMR1 epigenetic regulation and/or highlighting FMR1 genetic/transcriptional mosaicism in a population of FXS patient PBMCs (Additional file 2: Figure S1 and Additional file 3: Figure S2). This evidence concerns the gene FMR1 and fragile X syndrome.