Subsequently, another study from the same research group revealed that mtDNA methylation patterns and mitochondrial DNMT3A levels were abnormal in the skeletal muscles and spinal cord of pre-symptomatic ALS mice carrying mutations in the human superoxide dismutase 1 gene (SOD1), which included DNMT3A up-regulation, increased MT-RNR2 gene methylation and decreased D-loop region methylation [49]. Here, SOD1 is linked to amyotrophic lateral sclerosis.