A rare Cu/Zn superoxide dismutase mutation causing familial amyotrophic lateral sclerosis with variable age of onset, incomplete penetrance and a sensory neuropathy.

We present three members of a pedigree with familial amyotrophic lateral sclerosis (FALS) who have a rare mutation in exon 4 of Cu/Zn superoxide dismutase (SOD1) codon position 89, converting alanine to valine. This mutation was associated with incomplete penetrance and variable age of onset. The onset of the disease was late in two of our patients and early in the other. Two of our patients had symptoms and/or signs of an associated painful sensory neuropathy. The incomplete disease penetrance seen with this mutation (and others reported in the literature) emphasizes the potential value for obtaining an SOD1 genotype in patients with ALS, even if there is no apparent family history.