Peripherin is a Class III intermediate filament subunit found in both the peripheral and central nervous systems, though it is concentrated--as its name suggests--in the neurons of peripheral ganglia and their processes. Antibodies to peripherin can be used in identifying, classifying, and studying neurons in the nervous system. Peripherin is also a good diagnostic marker for ballooned axons seen in Lou Gehrig's disease and some neuronally derived tumors. Peripherin is also a major component of the cytoskeleton of PC12 cells, a widely used model system for studies of neuronal differentiation. Autoantibodies to peripherin are frequently seen in the sera of patients with diabetes. Peripherin is not related to peripherin-RDS, a photoreceptor protein associated with retinal degeneration and blindness.