You Can Inherit Mitochondrial DNA From Your Father After All

Your cells need energy to function, and they get most of that energy from mitochondria. Naturally, scientists have taken great interest in studying this cellular organelle, but we’re still encountering surprises. We’ve long believed that mitochondrial DNA is only passed down by mothers. A team of researchers from the US, China, and Taiwan has identified several families where that isn’t true. They have a mix of mitochondrial DNA from both maternal and paternal lines, which is pretty weird.

If you paid attention in high school biology, you probably learned mitochondria are the “powerhouse of the cell,” and not much else. Your cells use a molecule called ATP as an energy storage mechanism, and several metabolic processes in your body can produce it. However, mitochondria pump out by far the most ATP, making them essential to your cells. Mitochondria have their own genome separate from the DNA in the cell’s nucleus that controls everything else about you. The mitochondria and their DNA should all come from your mother — they’re from the original egg cell rather than the sperm. That’s apparently not the case for everyone, though.

Defects in mitochondria can lead to severe metabolic diseases, so doctors sometimes test mitochondrial DNA in patients. That’s what doctors at Cincinnati Children’s Hospital Medical Center did for one four-year-old boy with a suspected mitochondrial disorder. They found his mitochondrial DNA had abnormally high heteroplasmy — genes from different sources, both mother and father. Doctors next tested the boy’s family looking for the same abnormality, finding it in his mother, grandfather, and two great aunts.

The Cincinnati team led by Taosheng Huang reached out to other facilities around the world in search of other people with heteroplasmy in their mitochondria. They found two more unrelated family lines with the same peculiar pattern of mitochondrial inheritance. Children in these families seem prone to get a mix of mitochondria at conception, and mothers pass that mix on to their offspring. So, even someone without a “trigger” for this condition could still end up with mixed mitochondria.

Scientists are currently unsure how paternal mitochondria are getting into these cells; we just know that it’s happening. A fertilized egg cell should exterminate any paternal mitochondria, but some people may carry a mutation that makes that mechanism less effective. Whatever the cause, it looks like a very rare occurrence. The study authors say that maternal mitochondrial DNA is still “absolutely dominant.”

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