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Amyotrophic lateral sclerosis (ALS) is characterised by progressive muscle weakness and degeneration of upper and lower motor neurones. The risk of developing ALS is partly genetic and partly environmental. Approximately 10% of cases of ALS are familial and a number of causative genes have been identified.1 Many of the causative genes encode proteins that accumulate in cells in ALS. Mutations of the copper-zinc (Cu, Zn) superoxide dismutase type 1 (SOD1) gene account for approximately 20% of familial and 3% of sporadic ALS cases.
Over 150 mutations in the coding region of SOD1 have been found in patients with ALS worldwide, with variation of the frequency of SOD1 mutations in different populations. However, not all SOD1 mutations are pathogenic and there is a variety of clinical presentations of patients with pathogenic mutations. Furthermore, the different mutations have diverse effects on the structure of the SOD1 protein, and some cause no abnormality other than decreasing the net charge of the protein.
We now describe two sisters, from a family of Caucasian genetic background, with a novel SOD1 mutation, and unusual clinical features before the onset of weakness. The proband developed painful leg and hand cramps and leg stiffening in her sixth decade. After about 10 years, she …