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The article describes that link between somatic—not inherited—genetic mutations and the risk of schizophrenia.
To find out if these mutations are hereditary, the scientists had to find out if they were present in all the cells of the organism,
What these researchers have analyzed are precisely the mutations that are not inherited from the parents.
Thus, the experts examined the data of genotypes and markers of more than 20,000 blood samples from people with or without schizophrenia from the Psychiatric Genomics Consortium. Thus, they identified two genes —NRXN1 and ABCB11— that were correlated with cases of schizophrenia when they were altered in the womb.
Although NRXN1 (a gene that helps transmit signals throughout the brain) has been linked to this psychiatric condition before, here are the somatic, not inherited, mutations that link it to schizophrenia.
To find out if these mutations are hereditary, the scientists had to find out if they were present in all cells of the body, since somatic mutations are only seen in a fraction of cells. And that portion varies depending on when and where the mutation occurred.
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If a mutation occurs early in development, the variant is expected to be present throughout the organism in a mosaic fashion.
Based on this principle, researchers can identify somatic mutations that occurred early in development and are found not only in the brain, but also in a part of the blood cells.
This is how Chris Walsh explains it to SINC: “The moment of the event (the mutation) can be calculated by the proportion of cells that contain the mutation. If it occurs when there are only two cells in the embryo, you would expect it to be in half the cells; if it happens when there are four cells, it will be found in a quarter of the cells (approximately) and so on.
The author details that “the specific events described (NRXN1 and ABCB11) could be observed in more than 10% of the cells”, which convinced them that these mutations “occur at some very early stage and, therefore, would be present in all tissues, including the brain, since brain cells are separated from the blood much later.
The method used to examine them, according to the researcher, was “developed to study the early stages of blood cancer, which may be caused by this type of CNV variation that is limited to the blood.” But “we ruled out changes known to be associated with blood disorders, revealing fewer events that are present in a greater number of cells: this suggests that they were produced earlier and would be shared between blood and brain.”
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Beyond these findings, the study opens the door to continue identifying other acquired mutations that could be connected to schizophrenia. The experts say that since the study looked at blood samples, it will be important to look for more specific mutations in the brain that might have been too subtle or recent in a patient’s life for this test to detect. In addition, somatic alterations or duplications could be a risk factor to investigate in association with other pathologies, they suggest.
“With this study, we show that it is possible to find somatic variants in a psychiatric disorder that develops in adulthood,” Maury points out, “and this raises questions about what other disorders might be regulated by these types of mutations.”
