Paternal mitochondria
Doctors described the family inheritance of mitochondrial DNA from the father
Ekaterina Rusakova, N+1
Researchers have described a case of paternal inheritance of mitochondrial DNA in humans, according to the Proceedings of the National Academy of Sciences (Luo et al., Biparental Inheritance of Mitochondrial DNA in Humans). They found nine people from three families who inherited up to 76 percent of mitochondrial DNA variants from their fathers.
Mitochondria are found in most eukaryotic cells. Their main function is to provide cells with energy due to ATP synthesis, generation of electrical potential and thermogenesis. Mitochondria have their own small genome (the human contains 16,569 base pairs), which in most organisms, including humans, is inherited through the maternal line. However, in some organisms, including great tits, mice and humans, part of the mitochondrial DNA is occasionally inherited from the father. Earlier, American doctors described the case of a patient with mitochondrial myopathy, a hereditary disease that leads to muscle weakness and exercise intolerance. It turned out that the disease developed because the man had different mitochondrial genomes in different cells – from his father and from his mother. At the same time, there was a mutation in the paternal mitochondrial DNA, which caused the disease. However, the patient turned out to be the only family member with myopathy. His parents and sister were healthy, and, as the screening showed, his sister inherited mitochondrial DNA from her mother.
American, Taiwanese and Chinese researchers led by Paldeep Atwal from the Mayo Clinic in Jacksonville and Taosheng Huang from the Cincinnati Children's Hospital Medical Center described a family case of inheritance of the mitochondrial genome on the paternal side.
The first person who was found to have inherited the mitochondrial genome from his father was a four-year-old boy who was admitted to the Medical Center of the Children's Hospital in Cincinnati. He was diagnosed with muscle pain, hypotension, fatigue, which were associated with defects in the functioning of mitochondria. The rest of family A had other symptoms (in particular, grandfather had a heart attack, and sister had a speech delay), which doctors did not associate with mutations in mitochondrial DNA. The authors of the study sequenced the boy's mitochondrial genome, and although they did not find pathogenic mutations in it, they found 31 heteroplasmic variants. Heteroplasmy refers to differences in mitochondrial DNA sequences in one organism, sometimes even in one cell. Scientists became interested in the unusually high level of differences and began to analyze the mitochondrial DNA of other members of the A family. As a result, it turned out that four people inherited the mitochondrial genome from both their father (about 40 percent of the variants) and their mother.
Then the authors involved two more families in the experiment – B and C. In one of them, a 35-year-old man and a 46-year-old woman were diagnosed with diseases presumably caused by mutations in the mitochondrial genome. The researchers sequenced the mitochondrial genomes of the patients and made sure that they, like family members, contain a large number of DNA variants. When analyzing mitochondrial DNA from the remaining members of families B and C, the researchers found that two members of family B and three people from family C in different generations inherited not only maternal, but also paternal mitochondrial genomes. Moreover, one of the representatives of the C family inherited 76 percent of the variants from the father's mitochondrial DNA.
According to the authors of the work, their results show that in some exceptional cases, the transfer of the mitochondrial genome along the paternal line in humans is possible, although of course, inheritance of maternal mitochondrial DNA remains the main one. It is possible that the transfer of the paternal genome is accompanied by a mutation in the nuclear DNA gene, which is associated with the elimination of paternal mitochondrial DNA.
Theoretically, diseases caused by mutations in mitochondrial DNA can be treated if, at the conception of a child, the defective genome is replaced by a donor taken from another woman. The first child born of three parents was born in 2016 in Mexico, the second such case was reported by Ukrainian doctors at the beginning of last year.
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