Abstract
MicroRNAs (miRNAs) are a family of small, genome-encoded endogenous RNAs that are transcribed but not translated into proteins. They serve essential roles in virtually every aspect of brain function, including neurogenesis, neural development, and cellular responses leading to changes in synaptic plasticity. They are implicated in neurodegeneration and other neurological disorders. Complex interplay among multiple pathways including excitotoxicity, mitochondrial dysfunction, ionic imbalance, oxidative stress, and inflammation are involved in the mechanism of CNS degenerative disease including Alzheimer's disease (AD). Circulating miRNAs are largely stable in blood and may serve as diagnostic markers for CNS injury. This chapter presents the findings in human studies using blood serum, blood plasma, and CSF which indicate that individual or combinations of miRNAs can serve as important biomarkers in distinguishing AD and mild cognitive impairment (MCI) patients from controls. Appropriate miRNAs can differentiate between AD and MCI, and between mild and moderate-severe AD, and predict the progression of MCI to AD. They could potentially replace or be combined with the molecular markers of AD currently used in clinical practice.