AFF2 and fragile X syndrome: A CCG expansion repeat in the fmr1 gene at the fragile X instability site FRAXA (Xq27.3) may result in FXS [2], and it has been reported that expanded GCC repeats in the fmr2 gene at the FRAXE site (Xq28) can also trigger FXS but to a less severe degree than that of the fmr1 mutation [3,4].