People who carry a genetic mutation associated with Alzheimer's disease may develop AD earlier than people who do not, according to a new study. Scientists at the Keck School of Medicine of the University of Southern California have mapped the effects of that genetic mutation, showing how the Alzheimer's risk factor affects the living human brain. The discovery was detailed recently in correspondence published in The New England Journal of Medicine alongside five other studies focused on the TREM2 gene variant.
“Our lab studies the rate of brain tissue loss in elderly people, trying to discover factors that protect you as you age,” says Paul M. Thompson, PhD, the study's principal investigator. “We have never seen such a dramatic effect as with this genetic variant. If you carry this mutation, there is a wildfire of tissue loss in the brain.”
Healthy people typically lose less than one percent of their brain tissue a year, offset by normal tissue generation from mental stimulation, Thompson says. Symptoms of Alzheimer's begin to manifest when approximately 10% of the brain's tissue has eroded away.
Thompson and colleagues compared brain magnetic resonance imaging (MRI) scans of 478 adults (average age 76 years old) participating in the Alzheimer's Disease Neuroimaging Initiative over two years. One hundred had Alzheimer's disease, 221 had mild cognitive impairment, and 157 were healthy elderly adults. The researchers found that mutation carriers lost 1.4% to 3.3% more of their brain tissue than non-carriers, and twice as fast. The loss appears to be concentrated in the brain's temporal lobe and hippocampus, which play key roles in memory. Read the NEJM correspondence.