Cu/Zn superoxide dismutase activity in familial and sporadic amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease that is inherited as an autosomal dominant trait in approximately 10% of cases. Recently we and others identified several single-base mutations in the Cu/Zn superoxide dismutase (SOD1) gene in patients with familial ALS (FALS). Using single-strand conformational polymorphism, we studied the C to G mutation in exon 2 of the SOD1 gene (resulting in a leucine to valine substitution in position 38) in affected and unaffected members of a large Belgian family with FALS. We measured the SOD1 activity in red blood cell lysates in 14 members of this family, including the only surviving clinically affected patient. SOD1 activity of the family members carrying the mutation was less than half that of members without the mutation. In addition, in 11 patients with sporadic ALS and 11 age- and sex-matched controls, red blood cell SOD1 activity was normal. These studies indicate that SOD1 activity is reduced in these FALS patients but not in sporadic ALS patients. Moreover, this SOD1 enzyme abnormality is detectable years before onset of clinical ALS in carriers of this FALS mutation.