As we age, our organs begin to age as well. However, each organ matures at a different time, so the rate of aging is different. The central nervous system is among the slowest in aging. This is because they mature very late compared to other organs.
In the case of the brain, aging starts after the age of 40, and one nerve cell is destroyed every second, and 86,400 nerve cells per day are destroyed. Of course, when external factors such as drinking and smoking intervene, the extinction rate becomes faster. When aging progresses at a normal rate, about 1.2 billion brain cells out of 86 billion brain cells are destroyed over 40 years, resulting in the loss of about 1.4% of all brain cells. However, this does not significantly affect cognitive decline.
Therefore, if forgetfulness, which is commonly experienced in adulthood or old age, does not cause major problems in daily life. It is not classified as a disease right now. However, although it does not meet the criteria for a disease like Alzheimer’s, there are certainly cases in which memory loss is evident. In the past, no theoretical basis has been established to explain this, but diseases that can explain it have recently been discovered.
What Causes Forgetfulness?
Professor Peter Nelson of the University of Kentucky, USA, while autopsiing older adults who died of aging, found tissue features that were common to people with a history of memory loss that did not meet the criteria for Alzheimer’s disease. Oddly enough, Professor Nielsen started researching for a vocation and in 2018 published a condition called Limbic-predominant age-related TDP 43 encephalopathy (LATE). LATE occurs when a protein called TDP 43 is modified due to aging and accumulates in limbic brain cells, causing brain pathology.
Originally, TDP-43 (transactive response DNA binding protein of 43 kDa) is a normal protein that is abundantly present in brain cells and is involved in DNA expression and RNA transcription. TDP-43 has similar properties to prion, the causative agent of mad cow disease. In this way, the modified TDP-43 forms a non-decomposable mass by aggregating with each other in the cytoplasm outside the cell nucleus, which is its normal location. In other words, huge garbage bags that cannot be disposed of inside the cells float around, impairing normal cell functions.
Alzheimer’s disease is caused by an abnormal build-up of beta-amyloid, which impairs several aspects of cognitive function at the same time. Therefore, not only memory but also calculation, judgment, sense of space and direction, personality, language function, etc. are also deteriorated. This is because, in addition to the hippocampus, the parietal lobe, temporal lobe, and frontal lobe are destroyed at the same time even if there is a time difference.
However, in LATE, the lesions are mainly concentrated in the amygdala and hippocampus. The amygdala is responsible for the underlying risk and avoidance response, but it is not yet clear what symptoms are caused by the abnormality here. Because the hippocampus is an important circuit for long-term memory of short-term memory, due to its degeneration, cognitive function is clinically deteriorated mainly by deterioration of episodic memory. It can be seen that some severe forgetfulness is occurring. Of course, LATE can also lead to a decline in other areas of cognitive function in later stages, a condition similar to Alzheimer’s disease. However, while severe Alzheimer’s disease is rare in very old people (because Alzheimer’s disease makes it difficult to exceed 90 years of age), severe LATE is more often observed in very old age.
The incidence increases after the age of 80
The initial symptoms of LATE are very mild. For this reason, it is common for cognitive function tests performed just before death to be normal. The rate of progression of the disease is slower than that of Alzheimer’s disease, so memory deterioration is gradual. There are even cases where the diagnosis is clinically diagnosed as Alzheimer’s, but the autopsy changes the diagnosis to LATE.
It usually occurs after the age of 80 and is very common. Since it is in the early stages of the study, the statistics are different, but it is reported that at least 20% of people in their 80s and older, and up to 50% in some research centers. The prevalence also increases sharply in the age group 85 years and older. Since very few Alzheimer’s patients survive after the age of 90, LATE is more likely to become a problem by the age of 100. LATE is a relatively recently discovered disease. As Korea enters a super-aging society beyond an aging society, it is expected that practical research on LATE will be conducted in the future.
Help = Hidak Consulting Doctor Hanseung Lee (Neurologist at Herb Neurology Clinic)