However, if intermediate CAG 30–33 repeat expansion of ATXN2 also causes ALS in an autosomal dominant mode, then it might be expected that its prevalence in fALS cases would be higher than that in sALS cases (For example, the frequency of SOD1 mutations is higher in fALS than in sALS patients). Here, SOD1 is linked to amyotrophic lateral sclerosis.