APP and Alzheimer disease: Risk loci like the APOE ε4 allele and other genetic variants like amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) variants have been shown to increase the risk of developing AD [6], while RNA transcripts, including mRNA, ncRNAs, circRNAs, miRNAs, piRNAs and siRNAs, have also been identified in the blood and cerebrospinal fluid in research on AD pathology [7].