Because the ratio of affected to total chromosomes is expressed within a larger range of variability (current sample ranges from 27 to 88 with a SD of 19.9) than the percentage of lymphocytes expressing FMRP (current sample ranges from 0.34 to 0.51 with a SD of 0.05), it is reasonable to hypothesize that the former biomarker should be more sensitive than the latter to the cognitive and/or behavioral variability in the FXS female population. This evidence concerns the gene FMR1 and fragile X syndrome.