Rescuing Fmr1‐KO mouse with AAV‐based FMRP administration at an early stage (P0‐P5) has provided the first proof of concept of a gene therapy approach for FXS (Gholizadeh et al, 2014; Hampson et al, 2019), but also revealed that inappropriate levels of FMRP expression can lead to worsening of FXS phenotypes, possibly due to the fact that FMRP, like other RNA‐binding proteins, induces cellular stress when overexpressed (Mazroui et al, 2002). Here, FMR1 is linked to fragile X syndrome.