Researchers have found a genetic variant that raises the risk of Alzheimer's disease, can improve the brain function of carriers when they are younger.
"From an evolutionary perspective it makes sense," says Duke Han at Rush University Medical Center in Chicago.
Professor Han's work examined epsilon 4, a variant of a particular gene known as apolipoprotein E or APOE, reports New Scientist.
The epsilon 4 variant is the best-established genetic risk factor for Alzheimer's disease.
Having one copy increases the risk of developing Alzheimer's at least fourfold compared with people who have other forms of the gene. A person with two copies has up to 20 times the risk.
The plus points of epsilon 4 emerged several years ago. It was when Han's team scanned the APOE genes of 78 American soldiers. All had suffered traumatic brain injuries, many while serving in Iraq. Sixteen had at least one copy of epsilon 4. Han's team expected to find that these carriers would be in worse cognitive shape than their counterparts with different versions of APOE, given previous studies that showed elderly people with epsilon 4 fare worse after head injury. But the opposite was true: soldiers with the epsilon 4 allele had better memory and attention spans.
The study was reported in the Journal of Neurology, Neurosurgery and Psychiatry.
In another study, conducted in 2000, it was found that young women with epsilon 4 have IQs a few points higher than those with no copies of the variant and score 7 points higher on the non-verbal portion of a common intelligence test. The study was published in Neuroscience Letters.