Recent reports have shown heterozygosity for some twenty different mutations in the CuZn-superoxide dismutase (CuZn-SOD) gene in familial amyotrophic lateral sclerosis (FALS), and analysed samples from patients have shown decreased enzymic activity. Here we report homozygosity for an exon 4 mutation, Asp90Ala in fourteen patients among four unrelated ALS families and four apparently sporadic ALS patients from Sweden and Finland. The erythrocyte CuZn-SOD activity is essentially normal. Our findings suggest that this CuZn-SOD mutation causes ALS by a gain of function rather than by loss, and that the Asp90Ala mutation is less detrimental than previously reported mutations.
Four-hundred and fifty-one blood samples from Scandinavian patients with motor neuron disease were analysed for mutations in the CuZn-superoxide dismutase gene. Forty-one (9.6%) of the 427 patients with the amyotrophic lateral sclerosis (ALS) form of the disease were found to have a disease-associated mutation, and 14 of these patients were apparently sporadic cases. A mutation was found in 12 of the 51 families with recognized familial ALS. The five different mutations found (Ala4Val, Val14Gly, Asp76Tyr, Asp90Ala, Gly127insTGGG) have different genetic characteristics and are associated with very variable phenotypes spanning from rapidly progressing disease with only lower motor neuron signs to very slowly progressing disease with both the upper and lower motor neuron systems affected. The patients showed different sites of onset, though the progressive bulbar palsy form of the disease appears to be rare among patients with a CuZn-superoxide dismutase mutation. The progression of motor signs and symptoms followed the same basic pattern in patients with different mutations. Extra-motor system symptoms were frequent among patients with a CuZn-superoxide dismutase mutation. The results suggest that patients with mutations in the CuZn-superoxide dismutase gene constitute one disease entity. The Val14Gly and Asp76Tyr mutations have not been reported before, and the latter is the first mutation to be found in exon 3 of the CuZn-superoxide dismutase gene.
We describe 36 patients (six were apparently sporadic cases and 30 were cases from nine families) with amyotrophic lateral sclerosis (ALS) characterized by a distinct phenotype associated with homozygosity for an Asp90Ala mutation in the CuZn-superoxide dismutase gene. The presenting motor manifestation in all patients was paresis in the legs, with slow progression to the upper extremities and finally to the bulbar muscles. The age of ALS onset varied from 20 to 94 years, with a mean of 44 years. Mean survival time was 13 years for the 11 deceased patients. However, this is probably biased and untypical (low) when compared with the disease duration in the surviving patients, and when considering other medical complications in the deceased patients. The rate of progression was highly variable, even within families. All patients showed signs of involvement of both upper and lower motor neurons. Other neurological features included painful muscle spasms and paraesthesiae in the lower extremities. Two-thirds of patients experienced difficulty with micturition. Electrophysiological studies confirmed the slow progression and spatial distribution of clinical symptoms in the peripheral motor system. Furthermore, [corrected] potentials evoked by transcranial magnetic stimulation (MEP) were compared with those evoked by cervical or lumbosacral electrical stimulation and often revealed marked slowing of transmission in central motor pathways. In Sweden and Finland ALS patients homozygous for the Asp90Ala mutation constitute a phenotypically characteristic subset of motor neuron disease.
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