A piece of high school genetics, relied on for many kinds of genetic testing, has been found to have exceptions. Although mitochondrial DNA (mtDNA) is usually received from the mother, three families have been identified where people received some of their mtDNA, three quarters in the most extreme case, from their father. The finding can change the way we treat mitochondrial diseases and brings genetic testing to maternal ancestry into question.
MtDNA exists separately from the rest of our DNA, inside the thousands of mitocondria within each cell, rather than the cell nucleus. It is so widely accepted as being from the mother's side is sometimes known as the Gene Eve, the idea being that it can be traced back to some primeval mother of all living humans. Testing of mtDNA is used to identify maternal ancestry.
However, all that will have to change after Dr. Shiyu Luo of the Cincinnati Children's Hospital Medical Center published a paper in the Proceedings of the National Academy of Sciences.
Luo's first exception is a boy who at four was hospitalized with suggestive symptoms of mitochondrial disease. Sequencing of the boy's mitochondria revealed no disease-causing genes, but some oddities in the mtDNA that led Luo and colleagues to sequence other family members for comparison. Around 40 percent of the boy's mitochondria matched that from his mother's father, and only 60 percent came from his grandmother.
After testing other members of the same family, and other families with mitocondrial diseases, Luo found that, while parental inheritance is very rare, it has occurred at least 17 times in three tested families.