Copper/zinc superoxide dismutase 1 and sporadic amyotrophic lateral sclerosis: Analysis of 155 cases and identification of novel insertion mutation

Amyotrophic lateral sclerosis (ALS) is a progressive paralytic disorder resulting from the degeneration of motor neurons in the brain and spinal cord and leading to death within 5 years of symptom onset. The great majority of ALS cases are sporadic, with the familial form (FALS) representing fewer than 10% of all cases. Mutations in the copper/zinc superoxide dismutase 1 ( SOD ‐ 1 ) gene have previously been identified as the underlying cause of approximately 20% of FALS cases. As the familial and sporadic forms of the disease are clinically similar, we have sought to determine whether such mutations in SOD ‐ 1 underlie any sporadic ALS cases. We have screened 155 sporadic cases by single‐strand conformation polymorphism and have identified 4 sporadic cases that possess point mutations in exon 4 of the SOD ‐ 1 gene. Two of these mutations are identical to those previously reported in FALS cases. One mutation is novel, resulting in a frameshift at Val 118 due to the replacement of G (first base in the last codon of exon 4) by AAAAC. This mutation results in a truncated SOD‐1 protein due to the introduction of a stop codon three residues into exon 5.