Blood tests could predict onset of AD in normally aging and people with DS up to 10 years in advance in combining measures of amyloid-bêta proteins, proteins IRS-1 (involved in insulin signaling in the brain and commonly defective in people with AD), the presence of genetic variants APOE3 and APOE4 in blood plasma, and differences in miRNAs levels. Here, IRS1 is linked to Alzheimer disease.