People with the "Alzheimer's gene" begin to have memory declines tied to aging before they reach 60, even if they have no clinical symptoms of dementia, a U.S. research team reported on Wednesday.
In a separate study, a second team found that people who learned they had the gene were not emotionally scarred by it.
Both findings, published in the New England Journal of Medicine, offer new support for genetic tests for Alzheimer's disease, a mind-wasting condition for which there are few treatments and no cure. It affects 26 million people globally.
Several companies — including Iceland's Decode Genetics' DeCodeME, 23andME backed by Google Inc and privately held Navigenics — sell tests that allow people to learn if they have inherited the ApoE4 gene variant, which raises the risk of Alzheimer's by more than 50 percent.
A new study by Dr. Richard Caselli of Mayo Clinic Arizona and colleagues found people who had the ApoE4 gene variant showed signs of memory trouble at an earlier age than people who did not have the gene.
Caselli studied 815 healthy people aged 21 to 97 who were grouped according to their gene status.
They found people who had the ApoE4 gene were more likely to develop age-related memory trouble before age 60, and accelerated memory declines were worse in people who inherited the gene from both parents.
Having ApoE4 does not mean a person is doomed to have Alzheimer's, and a team led by Dr. Allen Roses at Duke University in North Carolina reported at an Alzheimer's conference earlier this week that a second gene closely linked to ApoE4 called TOMM40 also significantly raised Alzheimer's risk.
Roses said together, the two genes may account for 85 to 90 percent of inherited forms of Alzheimer's.
Doctors do not routinely recommend people get tested for Alzheimer's disease, partly because of fears that genetic testing would distress them.
Researchers from Boston University School of Medicine and colleagues found that was not the case.
They studied 162 healthy adult children of patients with Alzheimer's who asked to be tested for the ApoE4 gene.
The team measured test-related distress in both groups at six weeks, six months and one year, and found people who learned they had inherited the gene "showed no more anxiety, depression or test-related distress than those who did not," Boston University's Dr. Robert Green said in a statement.
Those who were told they had not inherited the gene "experienced considerable relief," Green added.
Green said people in the study were carefully screened for emotional problems and trained genetic counselors disclosed the information. "It is not the same thing as simply providing risk information to anyone who asks," he said.
Two of the researchers had received funding from a now-defunct genetics testing company.
Dr. Gary Kennedy, director of geriatric psychiatry at Montefiore Medical Center in New York, said he did not recommend testing unless patients had several close relatives — parents, brother or sister — with Alzheimer's.
He does not recommend people get tested on their own. "That study is with a whole genetic counseling team. You have a very solid safety net to catch the person if they get frightened by it," Kennedy said in a telephone interview.