MT-ND4 and Alzheimer disease: To determine whether the number of mitochondria per cell could account for the differences in the respiratory parameters between the two AD LCL subgroups, we measured mtDNA copy number by calculating the ratio of 3 mitochondria genes, including ND1, ND4 and Cyt B, to the nuclear gene, PK. As shown in Figure 8, the mtDNA copy number was not different between the two AD LCL subgroups; thus, the distinct respiratory parameters observed in the two AD LCL subgroups are not due to differences in mitochondrial number between the groups.