Dads (not just moms) can transmit mitochondrial DNA, according to a new provocative study

It has long been thought that people inherited mitochondrial DNA – genetic material found in cell mitochondria – exclusively from their mothers. But now, a new provocative study reveals that, in rare cases, dads can also transmit mitochondrial DNA.

The study found that 17 people belonging to three different families appeared to inherit the mitochondrial DNA from their mother and father. The radical results, from researchers at the Cincinnati Children's Hospital Medical Center, were then confirmed by two additional labs using different test methods.

If the results are valid, "that basically changes everything we believe about mitochondrial inheritance, which is huge," said Dr. Sajel Lala, clinical geneticist at Nicklaus Children's Miami Hospital. , who did not participate in the study. According to Lala, the results will have to be replicated by more research groups and published in additional scientific articles. But the results could have "major implications for [genetic] advice and the field of genetics in general ". [Genetics by the Numbers: 10 Tantalizing Tales]

The study was published yesterday Nov. 26 in the journal Proceedings of the National Academy of Sciences.

Although most of our DNA resides in the nucleus of our cells, a small amount is found in the mitochondria – the organelles that generate energy for cells. In most mammals, mitochondrial DNA is inherited from the mother, while the father's mitochondrial DNA would be destroyed shortly after conception.

Scientists have sometimes found exceptions to this rule in some animals – for example, some studies have shown that male mice and sheep can transmit mitochondrial DNA in rare cases.

But the question of whether men can also transmit mitochondrial DNA to their offspring is controversial. In 2002, Danish doctors published in the New England Journal of Medicine a case where a man seemed to inherit 90% of his mitochondrial DNA from his father. But no other case of this type has been reported over the next 16 years, which has led many researchers to believe that the 2002 results were the result of technical errors.

But all this changed when Cincinnati Children's researchers decided to investigate the unusual genetic test results of a 4-year-old boy. The boy was suspected of having mitochondrial disease – or a disease caused by mutations in mitochondrial DNA. When the researchers sequenced his mitochondrial DNA, they found no apparent mutation causing disease, but they noticed a very strange thing: it seemed like the boy had two sets of mitochondrial DNA.

Subsequent investigations revealed that the boy's mother had inherited the mitochondrial DNA from his father and mother (the boy's grandfather and grandmother) and that she had transmitted this mixed set mitochondrial DNA to his son.

When the researchers looked at the DNA of other family members, they found that overall, 10 people in the family – three generations – had inherited mitochondrial DNA "two-parent".

This led them to explore other unusual genetic test results from two unrelated families, where they found evidence of mitochondrial biparental DNA in seven other people.

"Our results clearly demonstrate two-way transmission of [mitochondrial DNA] in humans, against the central dogma of mitochondrial inheritance, "the researchers wrote.

The results also raise the question of "how many other cases of individuals with biparental [mitochondrial DNA] inheritances were considered technical errors, "the researchers said.

Indeed, it is not uncommon for doctors to ignore the strange results of mitochondrial tests, especially if the patient does not seem to be suffering from a known mitochondrial disease. "[When] we do not get the result we expected, so we're sort of left with that, "said Lala.

If the findings are proven, further research is needed to accurately determine how fathers are transmitting mitochondrial DNA and how often.

Understanding how this happens "will broaden our fundamental understanding of the inherited mitochondrial transmission process" and could lead to new ways to prevent the transmission of mitochondrial diseases, the researchers concluded.

Originally published on Science live.

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