MtDNA exists separate from the rest of DNA inside the mitochondria within each cell rather than the cell nucleus. Mitochondria is so accepted as being from the mother’s side it is often called the Eve Gene, theory being that it could be traced back to some primeval mother of all humans, and it is relied on for a variety of genetics testing. In surprising findings this theory has now been shown to have exceptions, this may change the way mitochondrial diseases are treated, and it brings genetic testing for maternal ancestry into question.
Cincinnati Children’s Hospital Medical Center has found the first exception in a 4 year old boy who was hospitalized for symptoms of mitochondrial disease. His mitochondria was sequenced which did not show any disease causing genes, but oddities in his mtDNA led the team to sequence other family member for comparison. The team found that 40% of the boy’s mitochondria matched his father, and only 60% came from his grandmother.
Other members of the same family were tested, and other families with mitochondrial diseases. The team found that while paternal inheritance is very rare it was also discovered at least 17 times in three tested families.
Embryos receive mtDNA from both parents but the father’s contribution is typically eliminated before birth, in a process of elimination that is not understood very well. Dr. Shiyu Lou and team team suggest that an abnormality in a nuclear DNA gene is responsible.
Mutant genes can often be found to be co-existing within cells with healthy versions, mutant genes are common and they can cause a range of disease, the severity of which being determined by proportion of mitochondria carrying the mutant gene. Mothers with low levels of bad mitochondria with few or no symptoms can pass on larger doses to her children with serious consequences.
Some algae, yeast, and plants get mtDNA from fathers, cases of partial paternal mtDNA have been found in fruit flies, sheep and mice. Previous claims of paternal mtDNA inheritance have turned out to be errors caused by mislabeling or contamination. Lou has had all sequencing conducted independently at two labs, using different techniques, as well as separate blood samples to reflect the extraordinary nature of her claims.
