Star Tribune 17 Jul 2016 By MELISSA HEALY Los Angeles Times
New research into the genetic underpinnings of Alzheimer’s disease offers fresh evidence that the devastating brain disorder may gain a foothold years before dementia sets in, and takes a key step toward earlier detection of the disease.
In a study that scoured the genes of healthy young people for the presence of variants linked to Alzheimer’s disease, researchers have found that those who carried many of the telltale gene variations had a smaller hippocampus — a brain structure that is crucial to memory-formation — than did their peers with few of the genetic variations.
While statistically significant, the association was somewhat weak. But it was clearly detectable in cognitively healthy study participants who were still very young — between 18 and 36 years old.
When a large population of older study participants without dementia underwent the same broad genetic query, the test was able to distinguish those with poorer memory and cognitive function from those whose mental faculties were still strong.
On average, researchers found that the more Alzheimer’s disease genetic variants an older study participant carried, the smaller his hippocampus and the greater was the presence in his brain of betaamyloid protein — the sticky stuff that forms brain plaques in those with Alzheimer’s disease. The study was published in the journal Neurology.
The genetic test, which queried the genome at several thousand sites that have been linked to Alzheimer’s disease, also detected with some accuracy participants who, over a three-year followup period, would go on to have Alzheimer’s.
The genetic test used in the latest study is unlikely at any point soon to be a useful predictor of who will develop Alzheimer’s and who won’t, experts said. For now, its principal use may be to identify people who are at unusually high risk of developing symptoms of dementia as they age. Those people might then be enrolled in clinical trials of therapies that could delay or disrupt the onset of Alzheimer’s disease’s most telling symptom — progressive loss of memory and cognitive function.
Heredity is believed to play a powerful role in Alzheimer’s risk. Certain variations in one gene, called APOE, appear to account for some of Alzheimer’s inherited risk — about 6 percent.