AF4/FMR2 (AFF) is a family of nuclear transcriptional activators that encourage RNA elongation. There are four genes in this family, all of which reside in the nucleus of the cells. The gene family includes AFF1/AF4, AFF2/FMR2, AFF3/LAF4 and AFF4/AF5q31. Within the family, the AFF2/FMR2 is silenced in FRAXE intellectual disability; while the other three gene families will form fusion genes as a consequence of chromosome translocations with the myeloid/lymphoid or mixed lineage leukemia gene in acute lymphoblastic leukemias. While different members of the AF4/FMR2 family are known for playing various roles in cells, they all commonly participate in the regulation of splicing and transcription.