Superoxide dismutase (glu100-->gly) in a family with inherited motor neuron disease: detection of mutant superoxide dismutase activity and the presence of heterodimers.

Superoxide dismutase glu100-->gly, a mutation known to be associated with familial motor neuron disease (familial amyotrophic lateral sclerosis) has been detected in one symptomatic and five of seven asymptomatic members of a family with a history of this disease. On average, the individuals with the mutation had 75% of normal red blood cell superoxide dismutase activity. Native polyacrylamide gels stained for superoxide dismutase activity showed two abnormal bands in the family members identified as carrying the mutation. This indicates that active mutant enzyme is present in red cells and forms stable homodimers and heterodimers with the normal chain. A silent mutation in exon 4, not associated with motor neuron disease, was also detected in one family member.