A variation in a gene called ApoE4 raises the risk of developing Alzheimer's disease by more than 50%. People with the gene can show age-related memory decline before they reach 60, even if they have no clinical symptoms of dementia. Researchers from the Mayo Clinic in Arizona studied 815 healthy people aged 21-97 and found that people with the ApoE4 gene variation showed signs of memory trouble at an earlier age than people without it. The declines in people's memories were worse in people who inherited the variation from both parents.
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