Sequencing and mtDNA target sequence comparisons. A: average reads by mitochondrial genome location. B: size distribution of cell-free mtDNA reads. C: CYB vs. ND1 target sequence reads. D: CYB vs. ND1 copy number in plasma by droplet digital PCR. E: linear regression of CYB vs. ND1 copy number. For A, B, and C: n = 18 subjects; E: n = 111 samples. CYB, cytochrome B; mtDNA, mitochondrial DNA; ND1, NADH dehydrogenase 1.