Our iTRAQ quantitative proteomics approach revealed significant low abundances of subunits NDUFA1, NDUFA2, NDUFA4, NDUFA5, NDUFA9, NDUFA10, NDUFB3, NDUFB6, NDUFB8, NDUFB11, NDUFS4, NDUFS7 and NDUFAB1 in the early onset AD. Here, NDUFA9 is linked to Alzheimer disease.