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 (or CP115), 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). Cataract is the most frequent cause of visual impairment and blindness worldwide. While congenital cataracts are less frequent than age related cataracts, if not treated promptly they can result in irreversible neural blindness. The frequency of non-syndromic congenital cataract is estimated to be 1-6 cases per 10'000 children with one additional case being diagnosed during childhood.