Interestingly, 4 out of the 6 mitochondrial proteins that decreased in AD in both human and mouse CSFs were also reduced in the AD serum (i.e. ALDH6A1, ETFB, SOD2, and PRDX3), highlighting their robustness as the AD biofluid signature (Fig. 6b, Fig. S4). Here, ALDH6A1 is linked to Alzheimer disease.