Like FXS, CCG repeat expansions in the 5′UTR of AFF2 (AF4/FMR2 family member 2, previously FMR2, MIM #300806) on chromosome X are associated with another X-linked ID disorder in males (FRAXE, MIM #309548) described in 1993 [30]. The gene discussed is AFF2; the disease is fragile X syndrome.