SOD1 and amyotrophic lateral sclerosis: When equal amounts of microsomal proteins were analyzed and although there were large variations in the expression amongst the human samples (Figure 4B), the AAK1 protein levels were statistically significantly lower in the ALS samples which included 4 sporadic (SALS) and 4 SOD1-linked mutations (A4V, G127X, D101G, and G93C) compared with those from the normal subjects (Figure 4C).