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DNA that must pass only from mothers can come from fathers, too



Fibroblasts or connective tissue cells. Nucleus blue, green mitochondria.
Image: NICHD (Flickr)

You probably learned two things about mitochondria in high school biology. First, they are the power stations of the chamber. Secondly, you can inherit them only from your mother. But the new study seems to be exacerbating this second point.

A group of researchers from the United States, China and Taiwan identified three unrelated families with members whose mitochondria contain DNA from both parents. Although this discovery may repeat the discussion about the nature of the inheritance of mitochondrial DNA, the researchers hope that it will open up new ways of treating diseases.

The story began when a four-year-old patient suffering from fatigue and muscle pain was referred to the doctor-scientist Taoshengu Huang at the Medical Center of the Children's Hospital of Cincinnati. Others suggested that the boy showed signs of mitochondrial disorder, so Juan ordered and analyzed the boy’s mitochondrial DNA and found an abnormally high level of “heteroplasma,” which means that different mitochondria appear to contain different genes.

Mystified, he sequenced the mitochondrial DNA of other members of the boy’s family, including his sisters, parents, grandparents and siblings of his parents and grandparents. It turned out that the boy, as expected, received his strange mitochondria from his mother, who shared a high level of heteroplasm. But further analysis showed that his mother, grandfather, and two of his great aunts inherited mitochondrial DNA from both parents.

Juan reached out to other laboratories, looking for families with members who also had high levels of heteroplasm. He found two with similar patterns, where some individuals seemed to inherit mitochondrial DNA from both parents, which mothers would pass on to their children. And to even more doubt, Juan enlisted the Medical College at Beilor to take independent blood samples and consistently determine the mitochondrial DNA of three families. Their results confirmed Huang.

These results are naturally provocative, since several other attempts to show mitochondrial DNA, transmitted from both parents or from father to child, turned out to be negative. Gizmodo has turned to several external sources for comment and will update the message when we hear the answer. It is unclear how male mitochondria turn it into an egg, since the egg cell destroys the mitochondria of sperm after fertilization. In a new article published in the Proceedings of the National Academies of Sciences, it is proposed that, perhaps, the mutation disables the ability to eliminate mitochondria of the egg.

This study probably does not have enormous implications for evolutionary times when the maternal inheritance remains “absolutely dominant,” the authors write, this is an exception to the rule. But Huang was more interested in what the result might mean to cure the disease.

You may be familiar with another project in which researchers produced a child from three parents – eggs from a donor, a kernel from the mother, and sperm from the father. This was done to ensure that the mother did not pass along Lee syndrome. “This is a very complicated and expensive procedure,” explained Juan Gizmodo. Perhaps if they can find a mechanism for transmitting the father's mitochondria instead of the mother, they will be able to offer these options without a tripartite procedure.

It seems sometimes hard to find solid rules in biology, even when it comes to the most acceptable facts.

[PNAS]

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