Notably, two rare FXS mutations, I304N (a missense mutation in the KH2 domain) and ΔRGG+CTD (a guanine insertion within the RGG box causing a frameshift and truncated isoform), that we previously shown to have different effects on translational repression (9), had opposing effects in the puromycin-induced mRNA•ribosome dissociation assay. Here, KCNG1 is linked to fragile X syndrome.