Despite what was previously thought, some mitochondrial DNA can be inherited from fathers as well as mothers, scientists have found. A study, published recently in PNAS, began when the Cincinnati Children’s Hospital Medical Centre tested a child showing signs of fatigue and muscle pain to see if he had a mitochondrial disorder.

The child showed signs of a heteroplasmy in his mitochondrial DNA, made up of contributions from both his mother and father. Upon further tests, the child’s sister also showed the same results.

Further tests revealed three unrelated multi-generation families with a high level of mitochondrial DNA heteroplasmy, ranging from 24% to 76% across 17 people. It is thought these individuals are very rare exceptions to the rule, probably due to mutations disrupting the mechanism preventing a father’s mitochondria being passed on to offspring.

Some scientists unrelated to the research suggested that the finding could open up new areas of research and change how the causes of certain mitochondrial diseases are searched for and identified.