FMR1 and fragile X syndrome: Also relevant is the finding that only about 35% of WT levels of FMRP were sufficient to detect behavioral improvement in Fmr1-KO mice treated with AAV-FMRP (2), and intriguingly, a similar level of residual FMRP expression in people with FXS was sufficient to attain a mean IQ of 85, the lower bound for normal IQ range (50).