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Author: Jean-Claude Muller, 穆卓Executive Editor at BtoBioInnovation  jcm9144@gmail.com

SPECIAL REPORT #20

LATE, a new form of dementia that mimics Alzheimer’s disease

In the latest issue of Brain, an international team of scientists and clinicians led by Peter Nelson at the University of Kentucky in Lexington, describe a new disease named LATE which stands for “Limbic-predominant age-related TPD-43 encephalopathy”, a disease striking people in their very late stage of life.

Dementia is an umbrella term used to refer to many types of neurodegenerative diseases, when it was thought that the majority of them were diagnosed as Alzheimer’s. Several recent studies pinpointed to the fact that thousands of patients diagnosed with Alzheimer’s actually didn’t have the disease. The study published in Brain suggests that a quarter of people age 85 and older have LATE, a disease with symptoms that mirror Alzheimer’s disease, though it affects the brain differently and develops more slowly. Scientists believe that the two diseases are frequently found together, and in those cases the cognitive decline will be steeper than when triggered by either disease alone While the underlying cause of Alzheimer’s disease is still controversial and mostly linked to the presence of amyloid plaques, LATE dementia is caused by deposits of a protein called TDP-43 in the brain.

TDP-43 is a protein that helps regulate gene expression in the brain and in other tissues.  When TDP-43 misfolds, due to a mutation in the DNA that creates that protein, it causes problems triggering dementia. It was found that misfolded TDP-43 not only causes dementia but also amyotrophic lateral sclerosis as well as frontotemporal lobar degeneration and does impair the amygdala and the hippocampus, the human brain’s thinking and memory centers. Recent studies found that misfolded TDP-43 protein is very common in elderly patients, but as for Alzheimer’s disease, there is currently no simple and reliable biological test to clearly identify the misfolding of proteins in a living person. Autopsies of patients above 80 have revealed that 20% of all patients had buildups of misfolded TDP-43 which is supposed to be the culprit in LATE.

“Recent research and clinical trials in Alzheimer’s disease have taught us two things : First not all the people we thought had Alzheimer’s had it; second it is very important to understand the other contributors to dementia” said Nina Silverberg, director of the Alzheimer’s Disease Centers Program at the National Institute of Aging in Baltimore.

These new findings are likely to progressively change the way dementia is characterized by physicians and moreover explain why so many new experimental treatments for Alzheimer’s disease have failed. “Treatment trials of drugs that are designed to work against Alzheimer’s disease will not have any efficacy against LATE and this has important implications for the choice of participants in future trials” said Robert Howard, Professor at University College in London. The remaining issue will nevertheless be how to discriminate LATE from Alzheimer’s disease in the absence of specific biological testing.

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