More than 99% of the vertebrate ocular lens is comprised of terminally differentiated lens fiber cells. Two lens-specific intermediate filament-like proteins, CP49 (also known as phakinin) and the protein product of this gene, filensin, are expressed only after fiber cell differentiation has begun. Both proteins are found in a structurally unique cytoskeletal element that is referred to as the beaded filament (BF). Mutations in this gene are the cause of autosomal recessive cortical juvenile-onset cataract. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq].