FMR2 is a 1311 amino acid nuclear protein belonging to the AF4 family. Expressed in the brain, placenta and lung, FMR2 exists as two isoforms produced by alternative splicing. Defects in the gene that encodes FMR2 have been found to be a cause of FRAXE, an X-linked form of mental retardation. Individuals expressing the FRAXE site also have more than two-hundred copies of a GCC repeat adjacent to CpG island, compared to six to thirty-five copies of the GCC repeat in a normal individual. It is believed that loss of FMR2 expression causes this GCC expansion of the FRAXE site.