SOD1 and amyotrophic lateral sclerosis: Interestingly, SOD1 knockout mice do not develop ALS, although they do exhibit some age-dependent distal motor neuropathy compared with SOD1G93A mice, which supports the notion that toxic gain of function may be responsible for the motor neuron degeneration in SOD1G93A mice since enzymatic activity is retained in SOD1G93A mutation[10].