NDUFB6 and Parkinson disease: These results are consistent with previous reports that mitochondrial cI activity is reduced in PD [19] and cI is a prime target of environmental toxins such as 1-methyl-4-phenyl-1, 2, 3, 6-tetra-hydropyridine (MPTP) and rotenone that inhibit respiratory energetics and produce oxidative stress [20]–[22].