Much of the hydrogen peroxide that is produced during oxidative cellular metabolism comes from the breakdown of one of the most damaging ROS, namely the superoxide anion radical (O2-). Superoxide is broken down by superoxide dismutases into hydrogen peroxide and oxygen. Superoxide is so damaging to cells that mutations in the superoxide dismutase enzyme can lead to ALS, which is characterised by the loss of motoneurons in the spinal cord and brain stem, possibly involving the activation of caspase-12 and the apoptosis cascade via oxidative stress.