People can have a brain full of Alzheimer's disease, but not have the dementia that typically goes along with it. By the numbers, this subset of people can have many plaques and tangles in the brain, enough to qualify them for a diagnosis of Alzheimer's disease, but in reality, they don't have the memory loss or other clinical symptoms of Alzheimer's.
In most cases, people have more and more symptoms of dementia as the plaque and tangle Alzheimer's disease lesions accumulate in the brain. And , most people who have normal memory and thinking are found to have very few plaques or tangles.
Yet, there's this outlier group, who should, by most definitions, have dementia due to Alzheimer's disease, but they are resistant.
In a new study by researchers from the Perelman School of Medicine at the University of Pennsylvania with colleagues from Rush University, published online in Neurobiology of Aging, the team investigated why these people are resilient to Alzheimer's and found several biological factors that help distinguish the resilient group from those with dementia. They discovered that synapses are preserved in resilient cases and found an increase in the number of brain cells called astrocytes, that may provide a protective response to the "toxic" effects of plaques and tangles.
The team also identified new biochemical targets that may be associated with resilient cognitive brain aging in the subset of people who have Alzheimer's pathology, which they'll investigate further, thanks to a new grant from the National Institute on Aging.
In a disease with no known treatments or cures, this will be one more angle researchers will pursue, to thwart the diseases' advances. While research continues to progress in understanding how plaques and tangles develop and cause damage in the brain, it is also important to understand how the brain can fight this damage and preserve cognition.
Arnold SE, Louneva N, Cao K, Wang LS, Han LY, Wolk DA, Negash S, Leurgans SE, Schneider JA, Buchman AS, Wilson RS, & Bennett DA (2012). Cellular, synaptic, and biochemical features of resilient cognition in Alzheimer's disease. Neurobiology of Aging PMID: 22554416