Some dads have broken a textbook genetic rule. Fathers in three unrelated families passed mitochondria — tiny energy factories found in cells — on to their children, researchers report.
Scientists have long thought that children inherited mitochondria exclusively from their mothers, since mitochondria from the father’s sperm are usually destroyed after fertilizing the egg. The new research, published online November 26 in the Proceedings of the National Academy of Sciences, suggests that in rare cases dads can contribute mitochondria too. For now, the consequences of inheriting mitochondria from both parents aren’t known.
Mitochondrial disease researcher Paldeep Atwal spotted the paternal signature after examining DNA from a woman who came to the Mayo Clinic in Jacksonville, Fla. DNA in a cell’s nucleus is inherited equally from both parents and contains all the genetic instructions for building a body. Mitochondria have their own DNA, too, that contains some of the genes needed for building and running the organelles. The woman’s cells weirdly contained two types of mitochondrial DNA, some from mom and some “from elsewhere,” says Atwal, who now runs a private clinic in Jacksonville.
Thinking the result was a mistake, Atwal and colleagues repeated the test. “The same thing came back the second time, and that’s when we started to get a little bit suspicious,” he says.
The researchers had DNA from both of the woman’s parents, so the team examined the father’s mitochondrial DNA, and found that he was the source of the mystery mitochondria. The woman’s brother also inherited mitochondria from their father. “We thought, ‘What on earth is going on here?’ ” Atwal says.
So Atwal got in touch with Taosheng Huang, a mitochondrial disease expert at Cincinnati Children’s Hospital Medical Center. It turns out that Huang had examined patients from two other families in which fathers had handed mitochondria down to their children. All together, the researchers found 17 people in the three families who inherited 24 percent to 76 percent of their mitochondria from dad.
“It’s real and a very interesting discovery, but I’m not surprised,” says Sophie Breton, an evolutionary biologist at the University of Montreal who was not involved in the work. Previous studies in plants and other animals have indicated that males sometimes pass on mitochondria. And in one human case, researchers found dad’s mitochondrial DNA in a man’s muscle cells, but scientists questioned whether the finding was a technical glitch or contamination.
There’s no question that Atwal, Huang and their colleagues have found people who have both mom’s and dad’s mitochondria in their cells, Breton says. “And we’ll probably find the same thing in further studies.”
Still “it’s not going to be a very common event,” says mitochondrial geneticist Douglas Wallace, head of the Center for Mitochondrial and Epigenomic Medicine at the Children’s Hospital of Philadelphia. Mothers will probably always be the primary source of their children’s mitochondria, Wallace says. But in a few rare cases, the biological system that normally slates paternal mitochondria for destruction may fail, leaving at least some of dad’s mitochondria to multiply.
Breton thinks in some cases the discovery might negate the need to make “three-parent babies,” children whose mitochondria come from donor eggs because their mothers’ eggs carry mitochondrial diseases . “If the mitochondria from the father can do the job, maybe we could stick with the two-parent baby situation.”
