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In medicine, the simplest diagnosis is often the right one. One notable exception to this rule, however, is the conditions that affect our brains as we get older.
Earlier this month, a research team led by scientists from the University of Kentucky gave a name to another disease causing dementia. They call this TDP-43 encephalopathy related to age-predominantly limbic-FIN. LATE can often be confused with Alzheimer's disease. It also causes memory loss, but its symptoms tend to evolve more slowly than Alzheimer's and only occur in adults over 80 years of age. The pathology at the origin of LATE is completely different from that at the origin of other forms of dementia. Rather than accumulating deformed amyloid plaques and clumps of tau (proteins normally appearing in the brain), as is the case for Alzheimer's disease, LATE leads to the formation of deformed proteins called TDP-43 in three regions of the brain: the amygdala, the hippocampus and the middle. Frontal gyrus. It is still unclear what causes TDP-43 to clump up outside the cell nucleus, where it is normally found in healthy people.
According to the team's research, described in the Brain review last month, estimates from autopsy studies suggest that TARD could occur in 25% of adults over 80 years of age. This could also be detrimental to attempts to develop treatments for other conditions, such as Alzheimer's disease: although it appears that the progression of TLA is relatively slow, it deteriorates much more rapidly at home. patients with ALL and Alzheimer's disease. "It's an additive," said Peter Nelson, a neuropathologist at the University of Kentucky and lead author of the paper.
By reaching a consensus on what is LATE, scientists can begin to identify biomarkers of the disease and, possibly, treatments. Perhaps more importantly, it means that they can better discern patients likely to participate in clinical trials for other types of dementia. The reason that so many Alzheimer's clinical trials have failed is probably due to the fact that some participants also had a delay.
LATE is yet another unique type of deterioration that causes dementia. Dementia is a disease that alters a person's cognitive functions – memory, behavior, decision-making – to the point of interfering with everyday life. Over the years, scientists have learned that there are several different causes of dementia, mainly due to an abnormal accumulation of deformed proteins. Although symptomatic dementia may seem similar in patients, the underlying causes may be totally different.
| Type of dementia | Typical age of the beginning | Notable symptoms | Pathology |
|---|---|---|---|
| Alzheimer's disease | 65 and over | Loss of memory, followed by a more general cognitive decline, such as difficulty concentrating or remembering instructions. | Accumulation of beta-amyloid plaque and entanglement of tau. |
| Late (encephalopathy TDP-43 related to the predominant limbic age) | 80 + | Loss of memory, but with slower progression. Often makes the memory symptoms of AD worse. | Clusters of proteins called TDP-43. |
| PART (primary tauopathy related to age) | 80 + | Loss of memory, deterioration slower than LATE. | Tau entanglements similar to those of Alzheimer's disease, but no amyloid plaques. |
| Vascular dementia | 50 + | Varied; inability to form new memories, disorientation, difficulty of reasoning and impaired judgment. Sometimes vision loss or difficulty speaking. | Tiny blockages of blood in brain cells and microstrokes throughout the brain. |
| Lewy body dementia | varied | Difficulty of motor control, memory loss and general cognitive decline. Parkinson's disease is a form of Lewy body dementia. | Malformed proteins of alpha-synuclein. |
| ARTAG (tau astrogliopathy linked to aging) | 80 + | More data needed. | Tau deformed on and around brain cells called astroglial cells. |
| Temporal dementia | 45 to 65 | Behavior problems, such as impulse control. | Degradation of the front of the brain (multiple causes). |
To further complicate the problem, people often suffer from multiple conditions that lead to dementia. In 2018, researchers at Rush University in Illinois published work suggesting that of a cohort of more than 1,000 participants who died of dementia, 78% had two different types. Fifty-eight percent of participants had three types of dementia and about one-third had four or more types of dementia. Although Alzheimer's disease occurred in about two-thirds of the participants, only 9% of them only amyloid plaques and tau tangles associated with the disease.
As long as dementia treatments can not target specific causes, they will likely continue to fail.
"The aged brain," said Nelson, "is the most complicated thing in the world."
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