Mitochondrial alterations in dorsal root ganglion cells in sporadic amyotrophic lateral sclerosis

Little information is available regarding the morphological changes in the mitochondria in amyotrophic lateral sclerosis (ALS). In particular, mitochondrial changes in dorsal root ganglion cells have not yet been examined. We therefore conducted an electron microscopic examination of the mitochondria in dorsal root ganglion cells in 11 sporadic ALS patients, and 12 age-matched, non-neurological control individuals in order to determine whether or not they are affected in ALS. In both the controls and ALS patients, unusual inclusion bodies were frequently observed in the mitochondria in the somata of the ganglion cells. The inclusions consisted of an aggregate of tubules measuring approximately 40 nm in diameter varying in size and number. Such inclusions were frequently present in the cristae and/or intermembrane space, often expanding to form large bundles in the dilated intermembrane space. These structures quite frequently protruded outward unilaterally or bilaterally and were partially surrounded by the outer membrane of the mitochondria. The number of inclusions was significantly higher in the ALS patients than in the controls (P < 0.0001). Regularly spaced transverse processes similar to the rungs of a ladder were occasionally observed in the intermembrane space, along with infrequent but markedly increased cristae and stubby mitochondria. We concluded that mitochondrial abnormalities may be involved in the degenerative processes in the dorsal root ganglion cells in sporadic ALS. These findings therefore suggest that ALS is a widespread, more generalized disorder than previously thought, and that the degeneration is not confined to the motor neuron system.