administration of the agent is to diagnose alzheimer 39 s disease in certain other instances the administration is to reduce expression of such microrna microrna expression profiles have been investigated in the brain tissues from ad patients it has been discovered that certain micro rna for example mirna 650 are altered in patients with ad see fig1 in certain embodiments the microrna is one or more selected from the group mir 515 3p mir 21 mir 576 mir 490 mir 187 mir 449 mir 646 mir 409 5p mir 518e mir 517c mir 320 mir 564 mir 191 mir 142 5p mir 501 mir 519e mir 489 mir 124a mir 218 and mir 650 in certain embodiments two or more microrna are selected or three or more microrna are selected in certain embodiments the sample is collected from a subject suspected of or at risk of having alzheimer 39 s disease in certain embodiments the sample is a blood sample obtained from pulmonary or systemic circulation measuring the quantity of microrna and microrna expression patterns can be done by a variety of methods including amplifying and or sequencing one two three or more of nucleic acids of seq id no 1 20 or unique portions e g greater than 30 20 10 nucleotide segment thereof in certain embodiments the disclosure relates to methods of analyzing samples for expression of microrna or rna disclosed herein.