RNA-binding protein. Might be involved in alternative splicing regulation through an interaction with G-quartet RNA structure. When splicing is inhibited, accumulates in enlarged speckles. Additional isoforms seem to exist. Brain (most abundant in hippocampus and amygdala), placenta and lung. The disease is caused by variants affecting the gene represented in this entry. It is caused either by silencing of the AFF2 gene as a consequence of a CCG expansion located upstream of this gene or by deletion within the gene. Loss of AFF2 expression is correlated with FRAXE CCG(N) expansion. Normal individuals have 6-35 copies of the repeat, whereas cytogenetically positive, developmentally delayed males have more than 200 copies and show methylation of the associated CPG island. Belongs to the AF4 family.