SOD1 and amyotrophic lateral sclerosis: In the present study, we investigated D-loop methylation levels and mtDNA copy number in peripheral white blood cells from a group of 63 ALS patients, including 36 sporadic patients negative for the major ALS gene alterations and 27 familial cases with a germinal mutation in SOD1 or C9orf72 genes, and 51 healthy sex- and age-matched controls.