A Gene Result Changes What an Alzheimer's Blood Test Can Tell You

A blood test that can flag Alzheimer's disease before symptoms appear predicts how soon those symptoms arrive more sharply when it is read alongside a common gene result, a Columbia University-led team reported on Sept. 9 in The Lancet Neurology.

The test measures p-tau217, a fragment of the tau protein that builds up as Alzheimer's damage accumulates. The team read it alongside each participant's APOE genotype, a gene linked to Alzheimer's risk, and compared carriers of the ε4 variant with everyone else. Together, the authors write, the two might help estimate the risk and the timing of cognitive impairment in people who have no symptoms yet. They point to people with a family history of dementia and say the pairing could guide who is monitored and when treatment begins.

Yuexuan Xu and Richard Mayeux of Columbia University and colleagues pooled individual records from seven long-running studies of older adults in Canada, the Dominican Republic and the United States. Of the 8,582 people in the baseline analysis, 4,569 had no cognitive impairment when their blood was drawn and were followed from there.

In that followed group, each one-standard-deviation rise in p-tau217 came with a 24% shorter time to cognitive impairment among ε4 carriers, against 13% among non-carriers. That is an association measured in studies that already existed, not a trial. The gap in who stayed free of impairment opened 3 to 4 years after the blood was taken and before any symptoms appeared, the paper reports.

p-tau217 can rise before any outward sign of the disease, the authors note, but people with similar levels and different genetic backgrounds may differ in when decline sets in. Closing that gap is what the pooled analysis set out to do. The work was funded by the National Institutes of Health.