Coronation Street star Jane Danson has said a new storyline, in which her character Leanne Battersby's son is diagnosed with a life-threatening illness, "could really break" her.
Three-year-old Oliver became unwell last month while in the care of his father Steve McDonald (Simon Gregson).
Doctors initially put this down to a febrile convulsion, but when Oliver suffers another seizure this week, he is rushed to hospital for tests, and diagnosed with a mitochondrial disorder, for which there is currently no cure.
The ITV soap's research team worked with The Lily Foundation, a charity that supports families and funds research into the disease, which occurs when mitochondria in the cells do not function properly.
They also consulted with Professor Robert McFarland from the Wellcome Centre for Mitochondrial Research in Newcastle.
Danson said: "We've worked closely with Liz Curtis at The Lily Foundation.
"It was harrowing hearing the story of what happened to her daughter Lily but also really amazing to hear how people come through this, how they support each other and learn to live again.
"It's almost too much to comprehend but I came away from the meeting bowled over by her bravery and how amazing she is as a human being.
"She shared with me how she felt emotionally, how she got through her days, how people rallied around her.
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"I've also read a lot of literature about how families cope around their children's diagnosis with life-limiting illnesses, looking at the human elements to their stories amidst all the medical speak and hoping I can get it right.
"It is quite overwhelming, I've been so lucky to have so many stories with Leanne over the last 20 odd years but this one feels different, this one could really break her and it feels like it's the one where I've got the most responsibility to get it right."
Leanne and Steve are not a couple, and Coronation Street producer Iain MacLeod said the storyline would challenge their respective partners.
He said: "In the end it will leave everyone permanently changed, but also stronger for it.
"Once they have been through the fire, these relationships that have been tested in this extreme adversity will be much stronger and life-changing, and life-long relationships."
Liz Curtis, chief executive and co-founder of The Lily Foundation said: "There is currently no cure for mitochondrial diseases, so those diagnosed face an uncertain future.
"We have been impressed with how sensitively the show's researchers and script writers have handled this, listening to those who have been affected by the disease and the doctors who support them.
"We see this as a very positive step in our ongoing fight to raise awareness about mitochondrial diseases, support affected families and fund research to find a cure."
ITV has halted production on Coronation Street and Emmerdale, due to the coronavirus pandemic, and reduced its transmission of both soaps to make the episodes which have already been recorded last longer.
Coronation Street continues on ITV.