[Familial amyotrophic lateral sclerosis and mutations in the Cu/Zn superoxide dismutase gene]

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder affecting primarily upper and lower motor neurons. In all cases of ALS, approximately 5-10% of cases are familial (FALS). Missense mutations in the Cu/Zn superoxide dismutase (SOD1) gene on chromosome 21 have been demonstrated in some families of FALS since 1993. We have also identified a novel missense mutation (substitution of Thr for Ala4) in exon 1 in a Japanese FALS family, and clarified the pathological findings of a patient in this family were typical of FALS with posterior column involvement. However, the mechanism by which the mutations in SOD1 lead to ALS is unknown. It is now clear that the mutations in SOD1 reduce total SOD activities only by 30-60%, and there is doubt whether a reduction in enzymatic function of this magnitude suffices to cause the neuronal loss. Recently, transgenic mice expressing the mutant SOD1 demonstrate motor neuron degeneration despite an increased level of SOD activity. The process of motor neuron degeneration in FALS might be mediated by some novel functions of the mutant SOD1 protein.