C10orf4, also known as FRA10A or FRA10AC1, is a 315 amino acid nuclear protein that is expressed strongly in kidney, liver, heart, brain and skeletal muscle. Defects in the gene encoding C10orf4 are characterized by an expansion of a polymorphic CGG repeat within the 5'-UTR of the gene; an event that is thought to cause folate-sensitive fragile site FRA10A expression. Expression of this mutated FRA10A protein may be associated with tumorigenesis, neurological disorders and mental retardation. C10orf4 is believed to be conserved between species. Five isoforms of C10orf4, all of which differ in their C-termini, are expressed due to alternative splicing events.