Which is a better predictor of memory loss?
Two tests are available to determine if you are at increased risk for getting Alzheimer’s disease: a test for a gene known as APOE4 and a brain imaging test called a PET scan. A recent study in the journal Neurology finds the brain scan is a better predictor.
The PET scan can detect a protein called beta-amyloid that is found in the plaques observed in the brains of people who are later diagnosed to have Alzheimer’s disease. The recent study performed both tests in 141 older people who had no cognitive impairment and then followed them for 18 months. Those with high levels of beta-amyloid in the brain were more likely to have a deterioration in mental function than those with the APOE4 gene.
Dr. Rudy Tanzi, the Joseph P. and Rose F. Kennedy Professor of Neurology at Harvard Medical School, isn’t surprised. “If you see high amounts of beta-amyloid on the scan, then you may already be on your way to the disease,” says Dr. Tanzi. Studies are under way to determine if people who have abnormal PET scans relatively early in life may benefit from treatments with donepezil (Aricept) or memantine (Namenda), drugs currently approved to treat Alzheimer’s disease. The results will be known in several years.
If a person has symptoms suggesting early Alzheimer’s disease, Dr. Tanzi thinks the PET scan can be very valuable. “If you have symptoms, then the PET scan can help determine if it’s dementia due to Alzheimer’s or some other reason such as atherosclerosis,” he says. As for the APOE4 gene test, Dr. Tanzi doesn’t believe it’s worthwhile. “The test is not reliable,” he says, “and it doesn’t point to the need for specific treatments.”