Experts Propose New Definition and Recommendations for Alzheimer-like Disorder
An international group of experts has proposed a new name, staging criteria, and recommendations for a recently recognized brain disorder that mimics Alzheimer disease and is marked by a proteinopathy caused by malformed transactive response DNA-binding protein of 43 kDa (TDP-43).
The term limbic-predominant age-related TDP-43 encephalopathy (LATE) was coined in an effort to raise awareness and kick-start research into this “pathway to dementia,” the experts wrote in a report appearing in Brain. “As there is currently no universally agreed-upon terminology or staging system for common age-related TDP-43 proteinopathy, this condition is understudied and not well recognized, even among investigators in the field of dementia research,” wrote the authors of the report, led by Peter T. Nelson, MD, PhD, of the University of Kentucky, Lexington.
LATE neuropathologic changes, associated with a progressive amnesia syndrome that mimics Alzheimer, are seen in > 20% of individuals aged > 80 years, according to large, community-based autopsy series. It coexists with Alzheimer disease in many patients, lowering the threshold for developing dementia, authors said.
The term LATE is designed to encompass several other terms related to TDP-43 pathology, including hippocampal sclerosis and cerebral age-related TDP-43 with sclerosis, Dr. Nelson and colleagues noted.
The TDP-43 protein is encoded by the TARDBP gene and provides several functions related to the regulation of gene expression, the authors wrote.
Misfolded TDP-43 was known to play a causative role in amyotrophic lateral sclerosis and frontotemporal lobar degeneration, the authors noted, and then was also identified in the brains of older individuals with hippocampal sclerosis or Alzheimer disease neuropathologic changes.
The authors proposed a 3-stage classification system for LATE neuropathologic change based on TDP-43 immunohistochemistry performed during routine autopsy evaluation of the amygdala, hippocampus, and middle frontal gyrus. The amygdala is an area affected early in the course of the disease (Stage 1), whereas involvement of the hippocampus represents a more intermediate stage (Stage 2), and the middle frontal gyrus is more affected in advanced stages of the disease (Stage 3), according to the schema.
Five genes have been identified with risk alleles for LATE neuropathologic changes, authors said. Of note, several groups have found that the apolipoprotein E ∑ 4 allele, known to be a risk factor for Alzheimer disease neuropathologic changes and Lewy body disease, is also linked to increased risk of TDP-43 proteinopathy.
There are no established biomarkers specific to TDP-43 proteinopathy yet, which hampers development of clinical trials designed to test interventions to treat or prevent LATE, Dr. Nelson and colleagues said in their report. LATE also could obscure the effects of potentially disease-modifying agents being tested in Alzheimer disease clinical trials, which can complicate the interpretation of study results, they added.
“Until there are biomarkers for LATE, clinical trials should be powered to account for TDP-43 proteinopathy,” they wrote. Dr. Nelson and coauthors reported no author disclosures.
Source: Nelson PT, Dickson DW, Trojanowski JQ, et al. Limbic-predominant age-related TDP-43 encephalopathy (LATE): consensus working group report. Brain. 2019;142(6):1503-1527.
Andrew D. Bowser, MDedge.com/neurology