'Axogenic' and 'somagenic' neurodegenerative diseases: definitions and therapeutic implications.

Neurodegenerative diseases are characterized by a relentless loss of specific groups of neuronal subtypes. Many of these diseases share similar molecular mechanisms and extracellular mediators of neuronal loss. We now suggest that neurodegeneration originating in the neuronal cell bodies (e.g. in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis) should be distinguished from that originating in the axons (e.g. in glaucoma, certain peripheral neuropathies and spinal stenosis). We propose that the former group of diseases be defined as 'somagenic' and the latter as 'axogenic'. Although axogenic disorders may share common symptoms and mediators of toxicity with somagenic disorders, they have distinct temporal, subcellular and signal-transduction features. We further suggest that, by adopting this classification of disorders based on pathophysiological processes, we will come to recognize additional diseases (in particular, those defined as axogenic) as being neurodegenerative and therefore possibly amenable to neuroprotective therapy.