Peripherin is a type III Intermediate filament (IF) protein expressed mainly in neurons of the peripheral nervous system (PNS). It is also found in neurons of the central nervous system (CNS) that have projections toward peripheral structures, such as spinal motor neurons. Its size, structure, and sequence/location of protein motifs is similar to other type III IF proteins such as desmin, vimentin and glial fibrillary acidic protein (GFAP). Like these proteins, peripherin can self-assemble to form homopolymeric filamentous networks (networks formed from peripherin protein dimers), but it can also heteropolymerize with neurofilaments in several neuronal types. This protein in humans is encoded by the PRPH gene. Peripherin is thought to play a role in neurite elongation during development and axonal regeneration after injury, but its exact function is unknown. It is also associated with some of the major neuropathologies that characterize amyotropic lateral sclerosis (ALS), but despite extensive research into how neurofilaments and peripherin contribute to ALS, their role in this disease is still unidentified.