SOD1 and amyotrophic lateral sclerosis: This type of familial ALS results in the death of motor neurons, similar to sporadic ALS, and is not caused by a change in enzyme activity.2,147 SOD1 is a 15.4 kDa protein and is ubiquitously found in human urine and difficult to distinguish between kidney derived and that from mutant SOD1 ALS-associated protein in ALS urine.