The report was concerned with the mechanism responsible for familial amyotrophic lateral sclerosis (FALS). In several clinical cases, a mutation was found in the enzyme superoxide dismutase (SOD), suggesting to the authors that reactions catalyzed by the mutants were involved in FALS. The mutant and wild-type SODs were expressed in yeast, and the mutants were found to catalyze some chemical reactions more effectively. Other measurements showed that the Cu2+ at the enzyme's active site interacted with chelators differently in the mutants (the chelators blocked the reactions catalyzed by the mutants but had the opposite effect with wild-type SOD). A cell-culture model of FALS was developed in which apoptosis was inhibited in cells modified to express wild-type SOD, resulting in cell survival. When the mutants were expressed in the cells, apoptosis was enhanced and the cells died. The authors reasoned that if reactions catalyzed at the Cu2+ in the mutants were important in FALS, then Cu2+ chelators should inhibit cell death in the cells expressing the mutant, and such was found to be the case. The conclusion was that reactions catalyzed by the mutants probably caused FALS.