LATE, also known as limbic predominant age-related TDP-43 encephalopathy, is a recently identified type of dementia that impairs social, cognitive, and memory abilities.

LATE is a separate condition with its own risks and causes, albeit it sometimes coexists with Alzheimer's disease or AD.

In a recent study, published in the journal Alzheimer's & Dementia, researchers at the University of California San Diego School of Medicine, with colleagues elsewhere, provide new insights into the pathology of LATE, which could help lead to the development of diagnostics for a disease that is currently poorly understood and very difficult to identify in living patients.

Specifically, the researchers, led by senior study author Robert Rissman, PhD, professor of neurosciences at UC San Diego School of Medicine, reported significantly elevated plasma levels of TDP-43, a DNA-binding protein that has previously been associated with other neurodegenerative diseases, such as frontotemporal lobar degeneration, amyotrophic lateral sclerosis and AD, though the last condition is much more commonly characterised by an accumulation of two other proteins: amyloid-beta and tau.

The study analysed levels of TDP-43 extracted from the exosomes secreted into the bloodstream by various cell types, including neurons and glial cells.

Exosomes are extracellular vesicles or sacs that transport DNA, RNA and proteins inside the cell until their release. Researchers analysed the brains of 64 patients post-mortem, 22 with autopsy-confirmed LATE and 42 patients who died without an indication of LATE.

The effect was detected only in astrocyte-derived exosomes, not neuronal or microglial. Astrocytes are a sub-type of glial cells that performs many essential functions in the central nervous system, from regulating blood flow to providing the building blocks of neurotransmitters. They outnumber neurons more than fivefold.

Effective treatment of all neurological diseases depends greatly upon early diagnosis. At the moment, however, LATE can only be diagnosed after death, and it is often confounded by the fact that living patients may have both LATE and AD.

The findings that increased plasma concentrations of TDP-43 could be a tell-tale indicator of LATE are encouraging, said Rissman.

"There is accelerating research into the utility of blood-based biomarkers, which can offer earlier diagnoses of these difficult conditions without resorting to current expensive, time-consuming and invasive methods," he said.

"Increased plasma concentrations of TDP-43 have been observed in other neurological conditions, but its correlation with cognitive dysfunction and disease progression is not well established. Much more research and investigation are needed."

Rissman added that leveraging the findings could lead to not only earlier diagnoses of dementia, but improved accuracy. "I think some of the issues with the failed AD trials so far are that LATE patients are getting into them. They would, of course, not respond to treatment because they don't have AD."