A new form of dementia that "mimics" the symptoms of Alzheimer's and is thought to affect about one in five older people has been recognized in an important scientific report.
The international review concluded that a substantial fraction of patients over the age of 80 who were presumed to have Alzheimer's disease suffer from a different brain disorder known as LATE. The unrecognized disease is likely to have an impact on public health comparable to Alzheimer's, the authors said.
The symptoms of the two diseases, including memory problems, cognitive decline and mood disorders, are very similar, but LATE progresses more slowly. Basically, LATE is caused by problems with a completely different brain protein and will probably require different medications to treat it in the future.
Nina Silverberg, director of the National Institute on Aging and co-president of the American magazine, said: "Recent research and clinical studies on Alzheimer's disease have taught us that not all the people we thought were suffering from Alzheimer's disease."
Robert Howard, professor of psychiatry of old age at University College London, described the work as "probably the most important document" on dementia in the last five years.
"Those of us who work in dementia have long been confused by our patients who have all the symptoms of Alzheimer's disease, but whose brain does not contain the pathological features of the condition," he said, adding that another mystery was the which is why some of the older patients have not progressed as quickly as would be expected with Alzheimer's disease.
"We now know that these baffling patients probably suffer from LATE and not Alzheimer's disease and that LATE could" mimic "Alzheimer's in about 20% of cases," he said.
While the basic biology of Alzheimer's is not yet fully understood, a telltale sign is the presence of sticky proteins called amyloid plaques that form clusters in the patients' brains, causing neuron death and consequent irreversible brain damage. However, autopsies of study participants revealed a subgroup of patients without these changes. In about 20% of all patients over the age of 80, the scientists found accumulations of a different protein, called TDP-43, which according to them is the culprit of LATE.
The results are unlikely to change the way dementia is currently diagnosed: the significant overlap in symptoms means that it is currently impossible for doctors to distinguish between the two conditions with confidence. However, the results could help explain why the search for a cure for Alzheimer's has so far proved to be futile: it is possible that positive results have been diluted by the inclusion of patients with a different disease.
"The drug treatment trials that are designed to work against Alzheimer's will have no effect against LATE and this has important implications for the choice of participants in future studies," said Howard.
James Pickett, head of research at the Alzheimer's Society, said: "This type of research is the first step towards a more precise diagnosis and personalized treatment for dementia, as we began to see in other serious diseases like breast cancer. "
The review is published in the journal Brain.
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