Additionally, as SOD1 knockout mice do not develop a paralysis phenotype (Reaume et al., 1996), nor do all SOD1 mutations cause a complete loss of dismutase function, and enzymatically inactive mutant SOD1 still causes motor neuron disease (Borchelt et al., 1994; Wang et al., 2002), it is widely accepted that mutant SOD1 acts through a toxic gain of function mechanism. The gene discussed is SOD1; the disease is motor neuron disorder.