Thus the significantly shortened seeding lag time found with tissue homogenates from tgSOD1G93A mice is not simply associated with a generic process of neurodegenerative disease but rather due to the presence of a specific species of SOD1, found in the spinal cord of tgSOD1G93A, which has similar seeding properties to recombinant SOD1 fibrils formed in vitro. The gene discussed is SOD1; the disease is neurodegenerative disease.