Any of the body’s organs and systems can be affected including the brain, heart, lungs, gut, liver and skin.
In the months to come Leanne and Steve will be forced to come to terms with the heartbreaking diagnosis which will leave Oliver with a life limiting illness for which there is currently no cure.
As for why Coronation Street decided to tackle this difficult storyline, producer Ian MacLeod said: “This is a story about a family coming to terms with the most difficult news anyone can face and the ways in which this strengthens and shatters relationships in unpredictable ways.
“Above all, we wanted to do justice to the stories of the many thousands of families who have to deal with diagnoses similar to Oliver’s, be it a mitochondrial disorder or another life-limiting condition.
“It is something that, as a society, we find difficult to talk about but which is all too common.
“The taboo around these illnesses can mean awareness is low, which means funding for research is low.
“Aside from telling a brilliant, moving and emotionally complex story, we really hope to draw attention to this subject to change this situation for the better,” he added.