SOD1 and amyotrophic lateral sclerosis: Concerning ALS, altered methylation levels in the mitochondrial 16S rRNA gene and in the D-loop region were detected in the spinal cord and skeletal muscle of human-SOD1 transgenic ALS mice, and these changes were paralleled by a significant reduction of the mitochondrial DNA methyltransferase 3a (Dnmt3a) protein levels [22].