In FXS participants, mean FMRP levels at visit 1 and visit 2 were 20.7 ± 23.0 fmol/μg protein and 18.0 ± 23.7 fmol/μg protein, respectively, in hair follicles compared to 27.3 ± 31.3 fmol/μg protein and 24.1 ± 41.8 fmol/μg protein at visit 1 and visit 2, respectively, in peripheral blood lymphocytes. This evidence concerns the gene FMR1 and fragile X syndrome.