A variation in a gene called APOE4 is found in about a quarter of the population. Those who have one copy have four times the normal risk of developing Alzheimer's disease and those who have two copies have ten times the risk. Researchers at Imperial College London used MRI (magnetic resonance imaging) scans to see what was going on in the brains of people with and without the variations in the gene. They found that even when they were just lying still people with the variations in the APOE4 gene had much busier brains than other people. When the participants in the study did a memory task those with the variation had more activity in a part of the brain called the hippocampus which is linked to long-term memory and navigation and is one of the first areas to be affected in Alzheimer's. The researchers thought that the extra activity in the brains of the people with the gener variation might cause them to wear out sooner although they stressed that not everyone with an APOE4 variation will go on to develop the condition.
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