Every participant in a new study had the biomarkers of Alzheimer's, but almost half — 49 percent — of people with a certain genetic variant had Alzheimer's dementia, compared to 29 percent of those without the variant.
Protein plaques and tangles have long been thought to be the cause of Alzheimer’s disease. Now, scientists are looking beyond those biomarkers at a certain genetic variant that could be a clue to the cause of Alzheimer’s related cognitive decline.
According to new research published in the journal Neurology, the genetic variation, found on the sixth chromosome, leads to changes in the metabolism of an an antioxidant called glutathione. The researchers believe these changes could be associated with thinning of the cerebral cortex, the brain’s control center and information-processing hub, responsible for brain functions like memory, association and thinking.
“Our study identified one significant single nucleotide polymorphism related to cognitive decline independent of amyloid-beta and tau protein deposits in the brain,” Dr. Yong Jeong, a study author from the Korea Advanced Institute of Science and Technology, said in a news release. “We showed that this genetic variation negatively affects thinking and memory skills, partly because it’s associated with thinning in the cortex of the brain.”
Genetic variants have been found in past research to protect people against the effects of amyloid and tau protein build-ups in the brain. One extremely rare genetic variation was recently found to protect a woman against the onset of symptoms from Alzheimer’s for several decades. Jeong’s research team suspects this variant may do the opposite.
The researchers studied a group of 486 people who all had deposits of beta-amyloid and tau — two harmful proteins that are linked to Alzheimer’s — in their brains. Some had normal thinking and memory skills, while others had mild cognitive impairment, and yet others had symptomatic Alzheimer’s.
Some performed worse on cognitive tests than others. Those poor performers all shared one thing that the rest of the group did not: a certain genetic variant. Researchers used genetic analysis to pinpoint gene variants that were associated with cognitive function independent of amyloid and tau.
On a cognitive test where the highest score was 30, those with the genetic variant scored an average of 25. Those without the variant had an average score of 27. Among those with the variant, 11 percent had normal cognition, compared to a quarter of those without the variant who had normal cognition. Almost half — 49 percent — of people with the variant had Alzheimer’s dementia, while only 29 percent of those without the variant had Alzheimer’s dementia.
To measure the thickness of each person’s brain cortex, a common measure of brain health, researchers looked at brain scans. People who did not have the genetic variation, on average, had a greater cortical thickness than the people who have the genetic variation.
“Deposits of amyloid-beta and tau proteins in the brain may be required for a diagnosis of Alzheimer’s disease, but the current thinking is that they are not by themselves enough to cause cognitive decline and dementia,” Jeong said. “Understanding the genetic mechanisms underlying the development of Alzheimer’s may lead to the development of new treatments for this devastating disease.”
Genetic variations — or single nucleotide polymorphisms — are common enough to serve as potential biomarkers that may help identify genes that linked to diseases. One of this study’s limitations was a small sample size; researchers say more study of this particular genetic variant as it relates to Alzheimer’s is in needed.