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Mosaic genetic mutations more common than thought


And textbook claims are incorrect, researcher says.

From The Scientist :

Mosaicism can result when a de novo mutation arises after an embryo is formed. Using newer, more sensitive sequencing technologies, researchers have recently begun to identify mosaic mutations.

Of these 107 mutations analyzed, seven (6.5 percent) were not detected in the parents’ germlines. …

“Given the limitations of current sequencing technologies, this [frequency of mosaic mutations] may be just touching the tip of the iceberg,” said Philip Awadalla of the Ontario Institute for Cancer Research and the University of Toronto, who works on human population and medical genomics but was not involved in the current study.

“The textbook knowledge that our genome is identical in all the cells of our body is probably not true,” Hoischen told The Scientist.

“We consider ourselves as ‘individual’ partially because our genomic makeup is unique,” said Goriely. “But we are multicellular organisms, containing many populations of cells precisely organized into different tissues and organs. This study suggests that some of our cells carry different versions of our genomes. . . . The implication of this finding is profound, both from a clinical and a philosophical standpoint.” More.

Note: The mutations resulted in developmental delay or disease.

Here’s the abstract:

De novo mutations are recognized both as an important source of genetic variation and as a prominent cause of sporadic disease in humans. Mutations identified as de novo are generally assumed to have occurred during gametogenesis and, consequently, to be present as germline events in an individual. Because Sanger sequencing does not provide the sensitivity to reliably distinguish somatic from germline mutations, the proportion of de novo mutations that occur somatically rather than in the germline remains largely unknown. To determine the contribution of post-zygotic events to de novo mutations, we analyzed a set of 107 de novo mutations in 50 parent-offspring trios. Using four different sequencing techniques, we found that 7 (6.5%) of these presumed germline de novo mutations were in fact present as mosaic mutations in the blood of the offspring and were therefore likely to have occurred post-zygotically. Furthermore, genome-wide analysis of “de novo” variants in the proband led to the identification of 4/4,081 variants that were also detectable in the blood of one of the parents, implying parental mosaicism as the origin of these variants. Thus, our results show that an important fraction of de novo mutations presumed to be germline in fact occurred either post-zygotically in the offspring or were inherited as a consequence of low-level mosaicism in one of the parents. (paywall) – R. Acuna-Hidalgo et al., “Post-zygotic point mutations are an underrecognized source of novel genomic variation,” The American Journal of Human Genetics, doi:10.1016/j.ajhg.2015.05.008, 2015.

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"The implication of this finding is profound, both from a clinical and a philosophical standpoint.” What makes this "profound"? I ask out of total ignorance, and kinda more interested in the "philosophical" part. But an explanation the "clinical" profoundness would be cool too. ppolish

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