A new form of dementia, which mimics the symptoms of Alzheimer’s, has been identified by clinicians and scientists, and estimated to affect as many as a quarter of people over the age of 85.

They’re calling the disease LATE, short for “limbic-predominant age-related TDP-43 encephalopathy,” and while it shares symptoms with Alzheimer’s, scientists believe the causes are entirely different, according to ScienceNews.org.

“This is a disease that really attacks the very latest portion of the human aging spectrum,” according to coauthor Peter Nelson, a neuropathologist at the University of Kentucky in Lexington.

With both memory issues and dementia, LATE bears a strong resemblance to Alzheimer’s. But scientists say that LATE is caused by the buildup of a protein called TDP-43 that spreads to parts of the brain involved in thinking and memory, like the amygdala and hippocampus. Alzheimer’s, on the other hand, is characterized by plaques and tangles in the brain. Unfortunately, the signs of LATE can’t be detected until after a patient dies. With no clinical tests to positively identify the disease, LATE is usually diagnosed when other conditions have been ruled out.

Until now, scientists have known the disease exists, and in the journal Brain on Tuesday, the authors named the condition in hopes that it will help doctors in diagnosis. The review suggests a large number of elderly patients diagnosed with Alzheimer’s are actually suffering from LATE.

To make things even tougher, the brains of elderly people often see several different problems that can contribute to dementia. This makes it difficult to attribute a condition to a specific cause like TDP-43. Often, doctors find signs of both Alzheimer’s and LATE in elderly brains.

“Those of us who work in dementia have long been puzzled by our patients who have all the symptoms of Alzheimer’s disease, but whose brains do not contain the pathological features of the condition,” said Robert Howard, University College London professor of old age psychiatry.

He called the new report “probably the most important paper” on dementia published in the last five years.

Because LATE mimics Alzheimer’s, the confusion may have led to some recent, misleading trials for Alzheimer’s drugs. If a drug would have been effective to treat Alzheimer’s, but was given to a patient that actually suffered from LATE, it would have falsely suggested that the drug is ineffective. A starting point for diagnosis of LATE could actually help advance efforts to treat Alzheimer’s.

According to Howard:

“Treatment trials of drugs that are designed to work against Alzheimer’s will not have any efficacy against LATE and this has important implications for the choice of participants in future trials.”

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