[Motor neuron diseases: a type of programmed cell death?]

Motor neuron diseases in humans, which include amyotrophic lateral sclerosis (ALS) and spinal muscular atrophies (SMAs), are characterized by motorneuron loss and chromatolysis in some or many remaining cells of the anterior horn of the spinal cord. Motorneurons are filled with phosphorylated neurofilaments, and ubiquitinated filamentous and granular inclusions which conform Lewy-like bodies in ALS patients. In addition, axonal balloonings filled with phosphorylated neurofilaments are usually observed in ALS patients with predominant signs of spinal motor neuron deficits and rapid clinical course. SMAs also occur in other species. Loss of motorneurons and chromatolytic cells filled with phosphorylated neurofilaments are the main pathologic findings in the ventral horn. In both humans and animals, loss of synaptic afferents is found in chromatolytic cells but not in normally-appearing motorneurons, thus suggesting that loss of synapses is a later event in motor neuron disease. These morphological features, together with the lack of c-Jun/AP-1 immunostaining and lack of staining with the method of in situ labelling of nuclear DNA fragmentation of dying cells, are different from those found during the process of naturally occurring (programmed) cell death in normal development. Although deletions in the SMN and NAIP genes located in 5q are found in patients with SMA, the cell death programme in SMA should not be considered as a mere persistence or reactivation of naturally occurring (programmed) cell death during normal development.