AFF2 and acute lymphoblastic leukemia: While AFF2/FMR2 is silenced in Fragile XE syndrome (FRAXE) associated with mental retardation, the other three members have been reported to form fusion genes as a consequence of chromosome translocations with the myeloid/lymphoid or mixed lineage leukemia (MLL) gene in acute lymphoblastic leukemias (ALLs).