In what researchers claim as the largest study of its kind, the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium aimed to identify genes that might protect against memory loss in old age.
Nearly 30,000 people over 45, who did not have dementia, were tested on their ability to remember words and paragraphs. Their performance on these tests was logged and researchers compared the entire genetic codes of subjects who had faired poorly on the tests with those who had done well.
They found that people who performed badly were more likely to carry certain genetic variants near to the Apolipoprotein E (ApoE) gene. ApoE has already been linked with Alzheimer's disease and, interestingly, the association was stronger in people above the age of 65.
In a separate sub-study using 725 post-mortem brain samples, the researchers found that people carrying these variants were more likely to have very early signs of the brain damage associated with Alzheimer's.
On a more positive note, two regions of the genome already known to contain genes involved in immune response were associated with a greater ability to recall word lists. The researchers say this finding 'provides new support for an important role of immune system dysfunction in age-related memory decline'.
Finally, the scientists examined post-mortem samples taken from the hippocampus - a brain area associated with memory, which is affected early on in Alzheimer's disease.
According to lead author Dr Stéphanie Debette from Boston University School of Medicine: 'The genetic variants associated with memory performance also predicted altered levels of expression of certain genes in the hippocampus.' The genes in question are involved in the metabolism of ubiquitin, which plays a vital role in regulating levels of cellular protein.
Professor Ian Deary, based at the University of Edinburgh, another lead author for the research, said he hoped that finding 'the small individual genetic variants that contribute to memory [...] will lead us to the mechanisms that underpin healthy cognitive ageing'.
The report was published in the journal Biological Psychiatry.