A clinical variance in familial amyotrophic lateral sclerosis with a point mutation in Cu/Zn superoxide dismutase gene

We report here a novel point mutation in exon 5 of the Cu/Zn superoxide dismutase (SOD) gene resulting in an amino acid substitution of valine¹⁴⁸ by isoleucine (V148I) in a Japanese family with amyotrophic lateral sclerosis (FALS). In this family, the age at onset was young (28.0 ± 3.8 years old, mean ± SD, n = 4) and the disease progression was rapid (22.0 ± 5.9 months, n = 3) with low Cu/Zn SOD activity (56.3 and 59.0% of the controls, n = 2). It is interesting that the clinical features of ALS varied very much among the affected members. One case had weakness of the lower extremities at first, and died without bulbar paresis. The second case first noticed wasting of the upper limbs with bulbar symptoms, but the third had weakness of upper extremities without developing dysarthria nor dysphagia until death. The living remainder first developed fasciculation of the tongue without weakness of extremities. The valine¹⁴⁸ is conserved among different species, and V148I mutation might destabilize dimer formation with another SOD subunit, leading to decrease enzymatic activity. These results suggested that there could be considerable clinical variance among the patients of FALS within one family, carrying the same Cu/Zn SOD mutation such as V148I.