Signs of Alzheimer’s seen in young brain’s GPS cells

Alzheimer’s disease may muck with people’s brains long before symptoms appear.

People in their early 20s with a genetic risk for Alzheimer’s have wonky internal compasses, despite showing no external signs of the disease, researchers report October 23 in Science.

This navigation tool rests deep in the brain, in a small, sausage-shaped region called the entorhinal cortex. Scientists could potentially examine it to detect Alzheimer’s in young people, says neuroscientist Francesca Cacucci of University College London. “In the future, when we have therapies that slow down the progression of Alzheimer’s, you could target the disease very early,” she says.

Currently there is no cure for Alzheimer’s, an irreversible memory disorder that typically shows early symptoms when people are in their mid-60s, according to the National Institute on Aging. In the last decade, the pharmaceutical industry has poured billions of dollars into developing new drugs for the disease, says study coauthor Nikolai Axmacher, a neuroscientist at the University of Bonn in Germany. But in clinical trials, the drugs have failed.  

“This is very likely because the drugs were delivered too late,” he says. For people who suffer from full-blown Alzheimer’s, the brain may be past the point of repair. So scientists have tried to find ways to diagnose the disease early.

Axmacher and colleagues looked for signs of trouble in the brains of young adults who have a copy of the e4 version of the APOE gene, a variant linked to risk for Alzheimer’s. The team scanned those adults’ brains, and the brains of people lacking the gene variant, as the participants performed memory tests while navigating through a virtual reality maze. With or withoutthe gene variant,the participants performed equally well — but the two groups used different parts of the brain. 

Healthy participants tapped into their entorhinal cortex, which holds cells involved in spatial navigation. These cells, called grid cells (SN Online: 10/6/14), help keep track of the direction people move.

In people with the e4 variant, the grid cells were hyperactive and “the directions were not stable,” says Axmacher — kind of like a compass with a needle that keeps fluttering around. These people recruited a neighboring part of the brain, the hippocampus, to get through the maze.

Navigation-wise, it seemed to work. But decades of relying on both regions could contribute to the development of Alzheimer’s, Axmacher says.