A study published in Acta Neuropathologica Communications found that a subgroup of people had clear indications of Alzheimer’s disease in their brain tissue, but they showed no symptoms while they were alive. Granted, they identified only 12 of these individuals from the available brain tissue with the necessary clinical information recorded.
Dementia directly affects more than 55 million people (about twice the population of Texas) worldwide, and up to 70% of those people have Alzheimer’s disease, which is characterized by a loss of brain cells associated with the toxic buildup of two proteins, amyloid and tau. The most common symptoms of Alzheimer’s disease are memory loss, cognitive deficits, problems with speaking, recognition, spatial awareness, reading, or writing, and significant changes in personality and behavior.Since Alzheimer’s is progressive, these symptoms are usually mild at first and tend to become more severe over time. The phenomenon of Alzheimer’s disease without symptoms is referred to as “resilience”.
Astrocytes can increase inflammation as they interact with microglia in the brain, but those pathways linked to Alzheimer’s seemed less active in the resilient group. Researchers also found that a brain cell response that is supposed to remove any misfolded toxic proteins was relatively normal in the resilient group.
This so-called “unfolded protein response” is generally affected in Alzheimer’s patients. There were signs that resilient individuals’ brain cells had more mitochondria than the cells of other Alzheimer’s patients, which meant energy production would have been stronger in the resilient group. Genetics and lifestyle can have a role in this type of resilience. The authors talk about changes in the function of neuronal support cells like astrocytes and microglia or the parts of neurons like energy-producing mitochondria.
Merrill said that adult children or spouses of people with Alzheimer’s may come in for testing without symptoms, but in general, most clinic patients seek care when symptoms appear. It’s not common to have patients without symptoms, be it Alzheimer’s disease or otherwise. Researchers saw more of a continuum of symptoms rather than a categorical phenomenon of symptomatic versus not. In that way, it makes sense that brain donors without any symptoms whatsoever were rarely observed in the study.
Markers of Alzheimer’s disease can begin quite early in life without the presence of typical symptoms. Doctors say that there are many people with pathological markers of Alzheimer’s disease without Alzheimer’s symptoms. Beta-amyloid, the pathological marker of Alzheimer’s disease, can start to accumulate in the brain as early as in the 20s. Amyloid deposition in the brain starts decades before the onset of Alzheimer’s symptoms. One study found that 44% of 90-year-olds with good cognitive function had amyloid pathology. There are also examples of genetic mutations that confer protection against a genetic form of Alzheimer’s disease.
