All DNAs are not identical, and science has long argued that your mother and father do not transmit all kinds of DNA. But it seems that the time has come to rewrite textbooks.
Although most of our DNA resides in the nucleus of the cell, part of our genetic code is stored in mitochondria, the so-called 'energy cell central'. The conventional view is that this mitochondrial DNA (or mtDNA) is inherited only from mothers, but new evidence suggests that this is not the case at all.
A new study led by geneticist Taosheng Huang of the Cincinnati Children's Hospital Medical Center shows that human mitochondrial DNA can be inherited paternally, in a landmark case that began with the treatment of cancer. a sick four-year-old boy.
The child, who showed signs of fatigue, muscle aches and other symptoms, was evaluated by doctors and tested to determine if he was suffering from a disorder. mitochondrial.
When Huang did the tests – and ran them again to be sure – he could not understand the results that had come back.
"It's impossible," he told NOVA Next.
The reason why Huang was so shocked was that the boy's results showed a mixture – called heteroplasmy – in his mitochondrial DNA, which consisted of more than mere maternal contributions.
Although there is evidence of paternal mtDNA transmission in other species, the existence of this phenomenon in humans has been the subject of debate, but has never been demonstrated before.
"It bothers entire areas based on genetics," said ecologist Trevor Branch of the University of Washington, who did not participate in the research. tweeted about the discovery.
When the boy's sisters showed signs of the same heteroplasmia, Huang and other researchers analyzed the mtDNA of the mother of the child, who also had the same mixture.
This led the team to analyze the mtDNA of the mother's parents, ultimately concluding that the mother's mtDM originated from a separation of about 60/40 respectively from her mother and father.
"Our findings suggest that, even though the central dogma of the maternal inheritance of the mtDNA remains valid, there are exceptional cases where paternal mtDNA could be transmitted to offspring," explain the authors. in their article.
But while these cases may be exceptional, they are not necessarily as rare as scientists might have thought.
In total, the researchers identified three unrelated multi-generation families with a high level of mtDNA heteroplasmia – ranging from 24 to 76% – in 17 distinct individuals.
Previously, two separate case reports at the beginning of the century had suggested the possibility of two-way transmission of tDNA, but no other evidence was presented for 16 years.
We now know that these results are not isolated and that sequencing technology is becoming more and more advanced, giving us a better tool to understand exactly what is going on here and how paternal transmission of 39, mDNA is common.
"It's a truly revolutionary discovery," said NOVA Next, a Stanford University biologist, Xinnan Wang.
"It could open up a whole new field … and change the way we look for the cause of [certain mitochondrial] diseases. "
The researchers argue that the strength of the first opinion – that only mother-to-child transmission was possible – could have meant that many cases of biparental transmission were previously overlooked as technical errors.
In any case, they suggest that their "clear and provocative" evidence should now initiate a broader assessment of the possibilities for tdDM, even though maternal transmission remains the norm.
"It is clear that these findings will have to be consistent with the fact that the maternal inheritance remains absolutely dominant over an evolutionary time scale and that occasional paternal transmission events seem to have left no detectable mark on the human genetic record, "writes the team.
"Nevertheless, this remains an unprecedented opportunity on the ground."
The results are reported in PNAS.