The High Court will hear fresh evidence in the case of terminally-ill baby Charlie Gard later.
Great Ormond Street Hospital (GOSH) has referred the case back to court after reports of new data from foreign healthcare facilities.
Charlie’s parents had made several unsuccessful challenges to a decision to end the 11-month-old’s life support.
On Sunday, his parents handed in a 350,000-signature petition calling for him to travel to the US for treatment.
Charlie inherited the faulty RRM2B gene, affecting the cells responsible for energy production and respiration and leaving him unable to move or breathe without a ventilator.
GOSH describes proposed experimental therapies as “unjustified” and said the treatments being offered are not a cure.
However, the hospital’s decision to go back to court came after researchers at two international healthcare facilities said they have “fresh evidence about their proposed experimental treatment”.
Charlie’s mother Connie Yates and father Chris Gard, from Bedfont in west London, want their son to have nucleoside therapy.
Speaking to BBC Breakfast, Ms Yates described the situation as a “living hell”.
“I couldn’t sit there and watch him in pain and suffering, I promise you I wouldn’t,” she said, adding: “I think parents know when their children are ready to go and they’ve given up and Charlie is still fighting.
“It’s horrible that this decision has been taken out of our hands, it’s not just about us knowing best, it’s about having other hospitals and doctors saying we want to treat [Charlie] and we think it’s the best thing to do.”
Ms Yates said they were not criticising Great Ormond Street Hospital as “they do great things”.
“But the children there, they’re all on treatment but our son isn’t so he deserves that chance too,” she added.
She said she hoped the judge would take into account new evidence as when the decision was made previously, his chance was rated at being close to 0% but now this has been increased to 10%.
“We have to stay strong and because our love for Charlie is so strong that’s what keeps us strong and when we have got hope we can carry on.
“I don’t know what we’ll be like if we lose him but we’ve just got to keep on, we can’t think about that.”
Analysis by Nick Triggle, BBC Health correspondent:
Charlie is thought to be one of 16 children in the world to have mitochondrial depletion syndrome.
It is a rare genetic condition which causes progressive muscle weakness and brain damage because he is unable to get energy to his organs.
Doctors have said he now cannot see, hear, move, cry or swallow and has irreversible brain damage. His lungs are only able to keep going because of the treatment he is receiving.
They have argued he should be allowed to die with dignity.
But his parents and supporters have been fighting for him to be given an experimental treatment in the US.
The treatment is not a cure – there isn’t one – but it has been suggested it could reduce the effects of the disease.
Although doctors in the US have since said the benefits they have seen have not been in cases as advanced as Charlie’s.
US President Donald Trump and the Vatican have supported the parents’ campaign for Charlie to be treated abroad, but a leading expert has described interventions from high-profile figures as “unhelpful”.
Professor Neena Modi, president of the Royal College of Paediatrics and Child Health said in an open letter that Charlie’s situation is “heartbreaking” for his parents, but added that even well-meaning interventions from outsiders can be unhelpful.
Mr Gard said: “If we won the court case and we got to America, and then within the first week of treatment he started suffering and he was in pain, we would let him go.
“This isn’t about us. This is about Charlie and giving him the chance he needs.”
Mr Justice Francis is due to hear fresh submissions on Monday afternoon.
- 3 March 2017: Mr Justice Francis starts to analyse the case at a hearing in the Family Division of the High Court in London
- 11 April: He says doctors can stop providing life-support treatment
- 3 May: Charlie’s parents ask Court of Appeal judges to consider the case
- 23 May: Three Court of Appeal judges analyse the case
- 25 May: Court of Appeal judges dismiss the couple’s appeal
- 8 June: Charlie’s parents lose fight in the Supreme Court
- 20 June: Judges in the European Court of Human Rights start to analyse the case after lawyers representing Charlie’s parents make written submissions
- 27 June: Judges in the European Court of Human Rights refuse to intervene
- 3 July: The Pope and US President Donald Trump offer to intervene
- 7 July: Great Ormond Street Hospital applies for a fresh hearing at the High Court