Background:The origin of amyotrophic lateral sclerosis (ALS) remains largely unknown but seems to be multifactorial. We believe that ALS clusters may help clinicians understand or analyze the role of environmental factors in ALS pathogenesis.

In a group of 331 sporadic amyotrophic lateral sclerosis (ALS) cases, we identified a new Cu/Zn superoxide dismutase single base substitution, N19S, in two patients. In the first case, seven healthy family members of 15 carried the substitution. Controls (n = 268) and familial ALS index cases (n = 180) were screened and one control subject with N19S was identified. Our data show that, despite a possible role of susceptibility factor for ALS, N19S alone cannot be considered as a direct cause for the disease.