Pathological TDP-43 translocation from the nucleus (red) to the cytoplasmic compartment occurs in sporadic disease and hereditary cases with C9orf72, TARDBP, GRN, and VCP mutations. VCP mutation cases also have intranuclear TDP-43 inclusions (not shown). C9orf72 mutation is associated with additional RNA foci in the nucleus (green) and cytoplasmic di-peptide repeat inclusions (blue), but the specific association with neurodegeneration is currently unclear. Neuron-to-neuron transmission is the likely mechanism for the non-random pattern of spread of neurodegeneration. These processes are linked to RNA dysfunction and abnormal proteostasis, ultimately leading to neuronal cell loss and/or muscle denervation from lower motor neuron loss. Drug-development efforts to slow or halt this process may provide novel disease modifying therapies in the future.