Combining presynaptic proteins, neuronal pentraxin 2 (NPTX2) and neurexin 2α (NRXN2α), with respective postsynaptic functional partners GluA4-containing glutamate receptor (AMPA4) and neuroligin 1 (NLGN1), and enhancing excitatory synaptic activities in areas of the hippocampus and cerebral cortex. As early damage of such excitatory circuits in Alzheimer's disease (AD) correlates with cognitive losses, plasma neuron-derived exosome (NDE) levels of these two pairs of synaptic proteins are quantified and serve as biomarkers. NDE contents of all four proteins decrease significantly in AD dementia and diminished levels of AMPA4 and NLGN1 correlate with the extent of cognitive losses. Prior to the onset of dementia, NDE levels of all but NPTX2 are significantly lower than those of matched control subjects and levels of all decline significantly with the development of dementia. Reductions in NDE levels of these excitatory synaptic proteins are indicators of cognitive losses and reflect progression of severity of AD.
