SOD1 and amyotrophic lateral sclerosis: Subsequently, the same group revealed that mtDNA methylation patterns and mitochondrial DNMT3A levels are abnormal in skeletal muscles and spinal cord of pre-symptomatic ALS mice that carry mutations in the human superoxide dismutase 1 gene (SOD1), including DNMT3A up-regulation, increased 16S rRNA gene methylation, and decreased D-loop region methylation (24).