Not just heredity
Scientists have named one of the main causes of dementia
Most cases of dementia may be associated not with hereditary factors, but with the appearance of new "point" mutations in a small set of genes in individual brain cells. Geneticists write about this in an article published in the journal Nature Communications (Keogh et al., High prevalence of focal and multi-focal somatic genetic variants in the human brain).
"The world's population is rapidly aging, and today more and more people are suffering from senile dementia. We still do not understand where these problems come from and why some of us become victims of them, while others do not. Dementia has a genetic background, but for some reason it does not affect heredity in any way," says Patrick Chinnery from the University of Cambridge, UK (in a press release from the University of Cambridge Many cases of dementia may arise from non-inherited DNA 'spelling mistakes' – VM).
The faded glow of the mind
Both Alzheimer's disease and Parkinson's disease are caused by the accumulation of various protein "garbage" in nerve cells, which gradually kills neurons in different parts of the brain. This leads to memory loss and senile dementia, as well as loss of control over the limbs with the development of Parkinson's disease.
The causes of these diseases and other forms of dementia are still a mystery to scientists. The search for their roots is complicated by the fact that only in five percent of cases of dementia, biologists and doctors find unambiguous hints that patients inherited these problems from their parents. This prevents the disclosure of the mechanisms of disease development and the identification of risk factors.
Chinnery and his colleagues found a possible explanation for all these oddities by analyzing how small mutations are distributed across different regions of the brain in about five dozen elderly people, some of whom suffered from "classic" dementia and Alzheimer's disease.
After selecting about two hundred tissue samples and 600 thousand cells, the scientists extracted DNA samples from them and read each of them five thousand times, eliminating the possibility of accidental errors when compiling a list of "typos" in the genome of neurons. After that, they isolated one hundred genes associated with the development of brain diseases and compared their structure in each brain sample.
Genetic Kaleidoscope
According to the researchers, they were interested in two things: whether the structure of these genes differs in cells of the same brain, and how often such "anomalies" appear. Their presence, in turn, suggests that these mutations were not inherited from the parents, but appeared after fertilization of the egg.
"These mutations appear in DNA during cell division, which may explain why many people become victims of Alzheimer's and Parkinson's diseases without having relatives with similar ailments. They are formed during the development of the embryo's brain and "sit in ambush", waiting for their owner to grow old," explains Chinnery.
As it turned out, such "typos", the so-called somatic mutations, existed in the brain cells of about half of the elderly people studied by the authors of the article. At the same time, they were present both in the nervous tissue of healthy participants in the experiment and in the neurons of carriers of dementia and Alzheimer's disease.
Later, scientists found out that these mutations did not occur randomly in the brains of sick and healthy elderly people. For example, senile dementia turned out to be associated with damage in the DNMT3A and TET2 genes that control the growth of brain vessels and the work of the barrier between the circulatory system and its tissues.
Further search for such somatic mutations in the brains of patients with dementia, scientists hope, will help to assess how much such new "typos" in DNA affect its development. This, according to Chinnery, is critically important for understanding whether the drugs that are being created today for the treatment of Alzheimer's disease will help the broad masses of people.
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