FMR1 and fragile X syndrome: An assessment of ID categories and FMRP levels (in pg FMRP/ng gDNA) showed that males with FXS and either mild or moderate ID had significantly higher levels of FMRP than those with severe ID (N = 15, 5.2 ± 3.8 versus N = 10, 2.3 ± 1.1; p = 0.013 and p = 0.019, respectively; Welch’s t-test and Mann–Whitney).