Of about 1500 miRNAs extracted from different biological matrices (blood, CFS, MCI, and the brain), 56 miRNAs showing significant differential expression in AD compared with the healthy controls and 10 novel miRNAs were found in the blood, and 2 of them were downregulated: miR-103, which is involved in neurite transportation, and miR-107, which is involved in BACE1 regulation. Here, BACE1 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.