Aberrantly occurring apoptosis may be the cause of motor neuron loss in ALS (23,98). Motor neurons undergo DNA fragmentation and are eliminated with minimal inflammatory changes (Figs. 8 and 9). In postmortem samples of ALS motor cortex and spinal cord, Bax and Bak protein levels are increased and Bcl-2 protein levels are decreased in mitochondrial enriched fractions. Co immune precipitation experiments demonstrate that Bax-Bax interactions are greater in the mitochondrial-enriched membrane compartment of ALS motor cortex compared to controls, whereas Bax-Bcl-2 interactions are decreased in the membrane compartment of ALS motor cortex compared to controls.