SOD1 and amyotrophic lateral sclerosis: Furthermore, a filter-trap assay using a 0.22 μm cellulose acetate membrane was examined to detect SOD1 aggregates in spinal cord homogenates containing Nonidet P-40 and sodium dodecyl sulfate; wild-type SOD1 aggregates trapped on the membrane were significantly augmented in the lumbar spinal cord of sporadic ALS cases (4 positive/7 total) compared with control subjects (0 positive/6 total) [42].